This study investigated the effects of screw diameter and length, loading, board material, board surface condition, and gluing, on moment resistances of three-screw L-type corner joints. Wood-based composite panels utilized in constructing joint specimens of this study were 18 mm in thickness. The joints evaluated in this study showed significantly higher moment resistances to loads that tended to open the joint than close the joint. Surfacing particleboard with synthetic resin and assembling joints with glue applied to the contact surfaces of the face and butt members of L-type joints significantly improved moment resistances of joints constructed of particleboard. Gluing improved the moment resistance of joints constructed of medium density fiberboard without resin surfacing, while no significant improvement was observed for medium density fiberboard with resin surfacing. The 5-mm-diameter by 50- or 60-mm-long screws yielded optimum moment resistances for joints in particleboard and medium density fiberboard, respectively.