Abstract: A method for inspecting the quality of modifiers for vinyl chloride type resins which includes kneading, with rolls, a soft vinyl chloride resin composition which is free of modifiers and is composed of a stabilizer, a plasticizer and a light shielding pigment to melt the composition and completely remove fish eyes present in the composition; adding a modifier for vinyl chloride type resins to the melted soft vinyl chloride resin composition; again kneading the mixture and then forming the mixture into a sheet to detect and count the number of fish eyes present in the sheet. This method makes it possible to simply and correctly determine the number of fish eyes of modifiers utilizing a widely used apparatus to thereby perform quality inspection of the modifiers. Moreover, when modifiers for vinyl chloride type resins are used in extrusion molding, the method is particularly effective for inspecting the quality of such modifiers.