The present invention relates to a resin composition for protective films which comprises an epoxy resin having two or more epoxy groups, a curing agent, a curing accelerator, a solvent, and a colloidal slurry of fine silica particles having an average particle diameter, as determined by conversion from the specific surface area, of 50 nm or smaller, a pH of 6 to 8, and an alkali metal content of 5 ppm or lower. The resin composition gives a protective film which satisfies adhesiveness and visible-light transmission, which are performances conventionally required. The protective film further has high surface smoothness even when the substrate surface is not smoothed. The resin composition has satisfactory storage stability and does not stain liquid crystal. Furthermore, a cured film obtained from the resin composition has excellent high-temperature resistance, especially ITO resistance. The resin composition is hence suitable for use in forming a protective film for the colored resin films of color filters for liquid-crystal display.