Laser ray transmitting colored polyolefin resin composition containing an anthraquinone salt forming dye below; and method of laser welding wherein welding a portion of contact of a laser ray transmitting material of said resin composition and a laser ray absorbing material by irradiating laser ray so that the laser ray transmitting material transmits the laser ray and the laser ray is absorbed in the laser ray absorbing material with the laser ray transmitting material and the laser ray absorbing material in contact with each other: A, B: —NH— or —O—; R1-R3: hydrogen, amino, hydroxy, halogen; R4-R13: hydrogen, alkyl, nitro, sulfonic group; Kin+: organic ammonium ion; m: 1 or 2; n: 1 or 2; the sulfonic group is —SO3 or SO3M, the number of —SO3 being m, M representing hydrogen or an alkali metal.