A method for producing a resin joined body in which a specific region L1 of a welding portion of a second resin member (21) is provided to form a low-laser-light-transmissible portion, and the low-laser-light-transmissible portion has a laser light transmissibility lower than that of a region of the welding portion other than the specific region L1. Welding is carried out so that a portion between points S2 and F2, serving as a weld overlap portion (112), is present in the specific region L1 forming the low-laser-light-transmissible portion. Also disclosed is a resin joined body.