The present invention relates to a resin composition and an optical compensation film formed by using same, and more specifically, to a resin composition comprising (a) an alkyl (meth) acrylate-based unit, (b) a styrene-based unit, (c) a 3 to 6-element heterocyclic unit substituted with at least one carbonyl group, and (d) a vynil cyanide, and to an optical film formed by using the resin composition. Also, the resin composition according to the present invention can provide the optical film having a superior optical property, optical transparency, little haze, and superior mechanical strength and heat resistance, and thus the optical film formed by using the resin composition can be applied to information/electronic devices, such as a display device, for a variety of purposes, and is especially appropriate as a compensation film which is used in an IPS mode.