A method and apparatus for molding plastic articles in two colors, particularly, the bodies of magnetic tape cassettes, in which a strong bonding force is provided between the two portions without having to form a recess and projection on the joining edges of the two portions. A slide core, which is moved in and out of a primary mold cavity between the mold of the two portions of the article, is provided with a tubular passage having an opening within the primary mold cavity along edge portions of the slide core. The slide core is fully inserted into the primary mold cavity to mold the first portion, then partially withdrawn to form a seconary mold cavity in which the second portion is subsequently molded. After molding the first portion, an adhesive is injected through the tubular passage along the edges of the first portion which will join corresponding edges of the second portion to thereby firmly join the two portions.