Abstract: A pistol laser sight mounting device comprises a base, a base cover, an L-shaped rod, and a receiving member. The base is provided with a retaining slot for disposing a pistol trigger guard, and with a first fastening portion. The basic cover is fastened with the base such that the retaining slot is sealed off by the base cover. The L-shaped rod has a fixed arm and a suspension arm. The fixed arm is provided with a second fastening portion which is fastened with the first fastening portion of the base. The receiving member is provided with two arm portions and a receiving through hole for holding the piston laser sight. The receiving member is fastened with the L-shaped rod by the two arm portions which are fastened with the suspension arm of the L-shaped rod.