diff --git a/lib/ocaml/eval.sx b/lib/ocaml/eval.sx
index 72e22faa..7835dd48 100644
--- a/lib/ocaml/eval.sx
+++ b/lib/ocaml/eval.sx
@@ -66,7 +66,30 @@
       ;; Print: prints to host stdout via println.
       (list "print_string"  (fn (s) (begin (print s) nil)))
       (list "print_endline" (fn (s) (begin (println s) nil)))
-      (list "print_int"     (fn (i) (begin (print (str i)) nil))))))
+      (list "print_int"     (fn (i) (begin (print (str i)) nil)))
+      ;; Hashtbl primitives (one-element list cell holding a dict).
+      ;; Keys are coerced to strings via `str` so any value type works
+      ;; as a key (matches Hashtbl's polymorphic-key semantics).
+      (list "_hashtbl_create" (fn (n) (list {})))
+      (list "_hashtbl_add"
+        (fn (t) (fn (k) (fn (v)
+          (begin
+            (set-nth! t 0 (merge (nth t 0) (dict (str k) v)))
+            nil)))))
+      (list "_hashtbl_replace"
+        (fn (t) (fn (k) (fn (v)
+          (begin
+            (set-nth! t 0 (merge (nth t 0) (dict (str k) v)))
+            nil)))))
+      (list "_hashtbl_find_opt"
+        (fn (t) (fn (k)
+          (cond
+            ((has-key? (nth t 0) (str k)) (list "Some" (get (nth t 0) (str k))))
+            (else (list "None"))))))
+      (list "_hashtbl_mem"
+        (fn (t) (fn (k) (has-key? (nth t 0) (str k)))))
+      (list "_hashtbl_length"
+        (fn (t) (len (keys (nth t 0))))))))
 
 (define ocaml-env-lookup
   (fn (env name)
diff --git a/lib/ocaml/runtime.sx b/lib/ocaml/runtime.sx
index 701dfb2c..8ad9cdc4 100644
--- a/lib/ocaml/runtime.sx
+++ b/lib/ocaml/runtime.sx
@@ -266,6 +266,19 @@
    module Printf = struct
      let sprintf fmt = fmt
      let printf fmt = print_string fmt
+   end ;;
+
+   module Hashtbl = struct
+     let create n = _hashtbl_create n
+     let add t k v = _hashtbl_add t k v
+     let replace t k v = _hashtbl_replace t k v
+     let find_opt t k = _hashtbl_find_opt t k
+     let find t k =
+       match _hashtbl_find_opt t k with
+       | None -> failwith \"Hashtbl.find: not found\"
+       | Some v -> v
+     let mem t k = _hashtbl_mem t k
+     let length t = _hashtbl_length t
    end")
 
 (define ocaml-stdlib-loaded false)
diff --git a/lib/ocaml/test.sh b/lib/ocaml/test.sh
index da64ab52..31587ac2 100755
--- a/lib/ocaml/test.sh
+++ b/lib/ocaml/test.sh
@@ -814,6 +814,20 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1506)
 (eval "(ocaml-type-of \"[true; false]\")")
 
+;; ── Hashtbl ────────────────────────────────────────────────────
+(epoch 1600)
+(eval "(ocaml-run-program \"let t = Hashtbl.create 10;; Hashtbl.add t \\\"x\\\" 42;; Hashtbl.find t \\\"x\\\"\")")
+(epoch 1601)
+(eval "(ocaml-run-program \"let t = Hashtbl.create 10;; Hashtbl.add t 1 \\\"a\\\";; Hashtbl.add t 2 \\\"b\\\";; Hashtbl.length t\")")
+(epoch 1602)
+(eval "(ocaml-run-program \"let t = Hashtbl.create 10;; Hashtbl.add t 1 100;; Hashtbl.find_opt t 99\")")
+(epoch 1603)
+(eval "(ocaml-run-program \"let t = Hashtbl.create 10;; Hashtbl.add t 1 100;; Hashtbl.mem t 1\")")
+(epoch 1604)
+(eval "(ocaml-run-program \"let t = Hashtbl.create 10;; Hashtbl.add t \\\"a\\\" 1;; Hashtbl.replace t \\\"a\\\" 2;; Hashtbl.find t \\\"a\\\"\")")
+(epoch 1605)
+(eval "(ocaml-run-program \"let t = Hashtbl.create 10;; Hashtbl.add t \\\"k\\\" 5;; Hashtbl.find_opt t \\\"k\\\"\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1288,6 +1302,14 @@ check 1504 "type fn -> list"              'list"'
 check 1505 "type fn -> tuple"             ' * '
 check 1506 "type Bool list"               '"Bool list"'
 
+# ── Hashtbl ─────────────────────────────────────────────────────
+check 1600 "Hashtbl find"                 '42'
+check 1601 "Hashtbl length"               '2'
+check 1602 "Hashtbl find_opt missing"     '("None")'
+check 1603 "Hashtbl mem"                  'true'
+check 1604 "Hashtbl replace"              '2'
+check 1605 "Hashtbl find_opt found"       '("Some" 5)'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index cef10f0d..961e5b05 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -248,6 +248,9 @@ SX CEK evaluator (both JS and OCaml hosts)
       `iter`, `fold`, `to_list`. _(Pending: join/to_result.)_
 - [~] `Result`: `map`, `bind`, `is_ok`, `is_error`, `get_ok`,
       `get_error`, `map_error`, `to_option`. _(Pending: fold/join.)_
+- [~] `Hashtbl`: `create`, `add`, `find`, `find_opt`, `replace`, `mem`,
+      `length`. Backed by a one-element list cell holding a SX dict;
+      keys coerced to strings via `str` for polymorphic-key support.
 - [~] `String`: `length`, `get`, `sub`, `concat`, `uppercase_ascii`,
       `lowercase_ascii`, `starts_with`. _(Pending: split_on_char, trim,
       contains, ends_with, index_opt, replace_all.)_
@@ -362,6 +365,10 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-08 Phase 6 — `Hashtbl` (+6 tests, 332 total). Backing store is
+  a one-element list cell holding a SX dict; keys are coerced to
+  strings via `str` so any value type can serve as a key. API: create,
+  add, replace, find, find_opt, mem, length.
 - 2026-05-08 Phase 5 — HM extensions for tuples and lists (+7 tests,
   326 total). Tuple type `(hm-con "*" TYPES)`, list type `(hm-con
   "list" (TYPE))`. `ocaml-infer-tuple` threads substitution through