A grooved resin molded part which when joined to another molded part, can form a composite molded product having an enhanced strength. This part contains an inorganic filler and has multiple grooves formed by partially removing the resin, such that the filler is exposed in these grooves. The depth of the grooves may be at least one-half of the length of the grooves in the shorter direction. The filler may have a fibrous shape; and the longer direction of the filler may be different from that of the grooves. The part is obtained by subjecting a resin molded part containing the filler to laser irradiation or the like to form multiple grooves in which the filler is exposed.