A cellulose acylate solution is used for producing a film in a solution casting method. Particles to be added to the cellulose acylate solution are silicon dioxide and surfaces of the particles are positively charged. After the particles are added to the solution, the filtrated solution is used for the film production. Thus the aggregation is prevented, and after the filtration pressure increases, the particles of large size are not contained in the filtrated solution. The obtained film contains a small amount of foreign materials and the situation of the film surface is good.