diff --git a/backend/app/services/market_presign.py b/backend/app/services/market_presign.py
index dce013c3..1e5ad132 100644
--- a/backend/app/services/market_presign.py
+++ b/backend/app/services/market_presign.py
@@ -740,13 +740,19 @@ def convert_presign_order(
             sales_user_id=row.sales_user_id,
             region_manager_user_id=row.region_manager_user_id,
         )
-        return presign_crud.convert_to_protocol(
+        result = presign_crud.convert_to_protocol(
             db,
             order_id=order_id,
             tenant_no=ctx.tenant_no,
             user_id=ctx.user_id,
             create_dept_id=_current_dept_id(user_info),
         )
+        if isinstance(result.get('presignOrder'), dict):
+            result = dict(result)
+            result['presignOrder'] = _mobile_order_to_dict(
+                db, row, ctx.tenant_no, with_children=True
+            )
+        return result
     except Exception:
         db.rollback()
         raise
diff --git a/backend/tests/test_market_presign_api.py b/backend/tests/test_market_presign_api.py
index 0a0e3535..81420c79 100644
--- a/backend/tests/test_market_presign_api.py
+++ b/backend/tests/test_market_presign_api.py
@@ -2304,3 +2304,80 @@ process.stdout.write(JSON.stringify(values.map(formatPresignMoney)))
         '-',
         '¥0.00',
     ]
+
+
+def test_mobile_presign_convert_response_preserves_decimal_for_presenter(
+    monkeypatch,
+):
+    import json
+    import subprocess
+    from decimal import Decimal
+    from pathlib import Path
+
+    from app.crud import presign_order as presign_crud
+    from app.services import market_presign
+
+    db = _session()
+    _add_master_data(db)
+    db.commit()
+    maximum = Decimal('9999999999999999.99')
+    order = _order('convert-money', sales_user_id='u1')
+    order.protocol_no = 'P-CONVERT-MONEY'
+    order.contract_amount = maximum
+
+    monkeypatch.setattr(
+        market_presign,
+        '_scoped_order_for_update',
+        lambda *_args, **_kwargs: order,
+    )
+    monkeypatch.setattr(
+        presign_crud,
+        '_get_order_or_raise',
+        lambda *_args, **_kwargs: order,
+    )
+    monkeypatch.setattr(
+        presign_crud,
+        'confirmed_deposit_amount',
+        lambda *_args, **_kwargs: maximum,
+    )
+    # SQLite binds Numeric through float. Keep the exact Decimal on the real ORM
+    # instance while exercising the complete core conversion and mobile response.
+    monkeypatch.setattr(db, 'commit', db.flush)
+    monkeypatch.setattr(db, 'refresh', lambda *_args, **_kwargs: None)
+
+    response = market_presign.convert_presign_order(
+        db,
+        order_id=order.id,
+        ctx=_ctx('specialist'),
+        user_info=_user(),
+    )
+    nested = response['presignOrder']
+    assert response['protocolId']
+    assert order.order_status == 'converted'
+    assert nested['contractAmount'] == str(maximum)
+    assert nested['confirmedDepositAmount'] == str(maximum)
+
+    presenter_url = (
+        Path(__file__).resolve().parents[2]
+        / 'mobile-oa-h5/src/market/presign/presign-presenter.js'
+    ).as_uri()
+    script = """
+import fs from 'node:fs'
+const { formatPresignMoney } = await import(process.argv[1])
+const dto = JSON.parse(fs.readFileSync(0, 'utf8'))
+process.stdout.write(JSON.stringify([
+  formatPresignMoney(dto.contractAmount),
+  formatPresignMoney(dto.confirmedDepositAmount)
+]))
+"""
+    formatted = subprocess.run(
+        ['node', '--input-type=module', '-e', script, presenter_url],
+        input=json.dumps(nested),
+        text=True,
+        capture_output=True,
+        check=True,
+    )
+    assert json.loads(formatted.stdout) == [
+        '¥9,999,999,999,999,999.99',
+        '¥9,999,999,999,999,999.99',
+    ]