You can set up a smooth preview in the 3D scene view and then render it.

1. In the Render Settings window, under Render Using, select mental ray.
2. Select the polyShape node for your mesh.
3. In the Attribute Editor, expand the Smooth Mesh section and select Smooth Mesh Preview.
4. Select the level of smoothing for your mesh by tweaking the division level. A higher value produces more smoothing. If you want to use the same division level for the 3D workspace preview as for your render, select the Use Preview Level for Rendering option. Otherwise, uncheck the Use Preview Level for Rendering option and use the Render Division Levels slider or text field to enter the desired division level for your render.