To provide an optical film having excellent optical properties and heat-resistance and usable as a substrate for a flat display such as a liquid crystal display.

The transparent film is composed of a fumaric acid diester resin and spherical inorganic particles such as colloidal silica having an average particle diameter of 200 nm. The spherical inorganic particle is preferably surface-treated with an organosilane compound or an organic compound containing a polymerizable group such as a (meth)acryloyl group, a styryl group and a vinyl group.