Disclosed is a process for manufacturing a polarizing plate protecting film comprising the steps of providing a film formation composition containing cellulose resin having a total acyl substitution degree of from 2.5 to 2.9, a plasticizer and a hindered amine or hindered phenol compound, heat-melting the film formation composition to obtain a melt, extruding the melt to be in the form of sheet, and cooling the extruded sheet to form a film, wherein the cellulose resin contains an alkaline earth metal in an amount of from 1 to 50 ppm and a residual sulfuric acid (in terms of sulfur content) in an amount of from 0.1 to 45 ppm, based on the weight of cellulose resin.