A laser-weldable polybutylene terephthalate-series resin composition having a high laser weldability is provided. The resin composition comprises (A) a polybutylene terephthalate-series resin and (B) a fatty acid-series compound (e.g., a C12-36 fatty acid ester, and a metal salt of a C12-36 fatty acid), and if necessary (C) a cyclic polyester oligomer (e.g., a cyclic polyalkylene terephthalate oligomer). In the resin composition, the proportion of the fatty acid-series compound (B) may be usually about 0.01 to 1.0 part by weight relative to 100 parts by weight of the polybutylene terephthalate-series resin (A).