A polyester elastomer resin composition that provides improved mold fouling in a continuous use for a long-term, and prevents the lowering in physical properties of polyester elatomer which causes by contacting with grease in environments exceeding 140° C. The polyester elastomer resin composition contains a thermoplastic polyester elastomer (A) prepared by bonding a hard segment and a soft segment an alicyclic polycarbodiimide compound and/or an aliphatic polycarbodiimide compound (B); and a polyamide resin (C) having an amine value of 50 to 2000 eq/tin such a ratio that (B) is in 0.1 to 5 part(s) by mass and (C) is in 0.1 to 10 part(s) by mass to 100 parts by mass of (A). The polyester elastomer resin composition has an acid value which is more than 5 eq/t and not more than 20 eq/t.