An LED mounting substrate includes a lead frame, a base, and a residue of injection molding material. The base is placed on the lead frame, and includes a cavity. The bottom of the cavity includes an opening for exposing portion of the lead frame. The cross-sectional area of the cavity increases along the direction from the lead frame to the top surface of the base. The residue of injection molding material is remained on one of outer walls of the base surrounding the cavity. The cross-sectional area of the residue of injection molding material decreases along the direction from the lead frame to the top surface of the base.