To obtain a resin composition for cleaning agent of molding machine capable of simply removing, in a short time, polymers of previously molded grade remaining in the molding machine after cleaning with the cleaning composition and cleaning with a small amount of polymer for substitution by formulating a specific ester forming complex and a metal compound to a thermoplastic resin.

This composition is obtained by formulating (B)(i) an ester of an aliphatic hydroxyl acid and an aliphatic alcohol, (ii) an ester forming complex with boric acid (e.g. the complex of the formula) and (C) one or more kind of metal compounds selected from a metal oxide, a metal hydroxide, a metal carbonate, a metal phosphate, a metal silicate, hydrotalcites or lithium aluminum complex hydroxide, a metal salt of aliphatic acid, a metal salt of an aliphatic hydroxyl acid, a metal salt of aliphatic phosphate (metal is lithium, sodium, potassium, magnesium, calcium, zinc or aluminum), in (A) a thermoplastic resin.