PURPOSE: To obtain a resin composition, containing a polyolefin (polyethylene), used for dispersing and finely dividing an additive and stably dispersed in a fine state in a base resin and good in moldability in spinning or forming a film.

CONSTITUTION: This resin composition comprises (A) an additive such as a pigment or an antimicrobial agent, (B) a polyethylene (PE) composition comprising a polyethylene having ≤7000 molecular weight and a polyethylene having ≥7000 molecular weight, (C) a copolymer comprising maleic anhydride and styrene and (D) a resin such as a thermoplastic polyester or a polyamide and the concentration of the additive is 0.01-5wt.%. In the composition, the copolymer (C) is present in an amount of 5-100wt.% based on the amount of the PE composition (B) used to thereby make the PE particles exist in a fine particulate state in the base resin (D). Furthermore, the method for producing the resin composition is to prepare an additive concentrate comprising the additive (A) and the PE composition (B), then mix and disperse the resultant concentrate in a composition containing the copolymer (C) and the resin (D).