To obtain the subject inexpensive composition excellent in flame retardance without emitting toxic gases when burning by blending a polyolefin- based resin with specific amounts of a phenol resin, a phosphorus-containing compound and an expandable graphite having a specified grain diameter.

This resin composition is obtained by blending 100 pts.wt. polyolefin-based resin (e.g. polyethylene) with (A) 5-30 pts.wt. phenol resin (e.g. a phenol novolak resin), (B) 5-50 pts.wt. phosphorus-containing compound (e.g. ammonium phosphate), (C) 1-30 pts.wt. nitrogen-containing compound (e.g. melamine cyanurate) and (D) 5-50 pts.wt. expandable graphite and melt kneading the prepared blend. The redultant composition contains no halogen, and hardly causes any deterioration in resin characteristics without emitting toxic gases when burning while retaining excellent flame retardance and is useful for various containers, tableware, toys, daily necessaries, sundries, kitchen utensils, film and sheet, automotive bumpers, etc.