A method for manufacturing a polarizing plate protective film including the steps of: 1) mixing a cellulose ester resin and an organic additive to obtain a mixing composition, 2) placing the mixing composition in a mold to obtain an integral molding, and 3) heating to melt the integral molding so as to form the polarizing plate protective film, wherein the integral molding has a size of 1 mm×1 mm×1 mm to 20 mm×20 mm×20 mm, and the cellulose ester resin is contained in the integral molding in a state of particles.