PURPOSE: To obtain a resin composition prevented from forming mold deposits by mixing a polyacetal resin with a specified lubricating oil, a melamine/ formaldehyde polycondensate soluble insoluble in warm water and soluble in dimethyl sulfoxide and an antioxidant.

CONSTITUTION: Melamine is reacted with formaldehyde in a molar ratio of 1/0.8 to 1/5 to prepare a melamine/formaldehyde poly-condensate insoluble in warm water and soluble in dimethyl sulfoxide. 100 pts.wt. polyacetal resin is mixed with 0.1-10 pts.wt. at least one lubricating oil selected from among a silicone oil, a perfluoropolyether, a polyalkylene glycol, an α-olefin oligomer, a paraffin oil, a 12 C or higher alkyl-substituted diphenyl ether and an ester of a 16 C or higher aliphatic alcohol, 0.01-10 pts.wt. above melamine/ formaldehyde polycondensate and 0.01-5 pts.wt. antioxidant. The resultant composition is melt-kneaded to obtain the objective composition which does not form any mold deposits.