The invention provides a decomposable resin composition, which is stable at the time of use and which quickly decomposes when discarded. According to the present invention, there is provided a resin composition comprising an agent generating an acid or a base upon response to light or heat together with a hydrolyzable and biodegradable resin. The decomposable resin composition can promote decomposition of the polymer by generating an acid or a base in the resin by carrying out light irradiation and/or a heat treatment at a desired time and can control the decomposition speed of the polymer by controlling the generation amount of an acid or a base.