Abstract: An optical film applied in a backlight module is provided. The optical film includes a basic layer, a plurality of periodically arranged reflective convex-parts and a plurality of periodically arranged collimating parts. The reflective convex-parts are disposed on the first surface of the basic layer. The reflective convex-part includes at least one reflective side surface and an incident bottom surface contacting a light guide plate. The collimating parts are disposed on the second surface of the basic layer. The reflective convex-parts are respectively corresponded to the collimating parts. In each corresponding pair of the reflective convex-part and the collimating part, a central axis of the reflective convex-part is substantially coincided with a central axis of the collimating part. In addition, a backlight module using the optical film is also provided.