The cross-linkable, foamable polyolefin resin composition capable of forming foams with excellent mechanical properties and heat resistance is made of (a) .[.30-80.]. .Iadd.14-80 .Iaddend.weight % of a propylene-ethylene random copolymer having an ethylene content of 1.5-6 weight %; (b) 10-60 weight % of a propylene-ethylene random copolymer having an ethylene content of 0.2-1.0 weight %; (c) 10-60 weight % of a linear low-density polyethylene; and (d) 1-30 parts by weight, per 100 parts by weight of the above resin components, of a foaming agent.