An A-site-ordered perovskite LaCu3Pt3.23O12 was synthesized by replacing Ca2+ with La3+ in a cubic quadruple AA(3)'B4O12-type perovskite CaCu3Pt4O12 under high-pressure and high-temperature of 15 GPa and 1100 degrees C. In LaCu3Pt3.75O12, 1/16 of B-site cations are vacant to achieve charge balance. The B-site deficiencies were evidenced by crystal structure refinement using synchrotron X-ray powder diffraction, hard X-ray photoemission spectroscopy, and soft X-ray absorption spectroscopy, leading to the ionic model La3+Cu32+Pt3.754+O122-. Magnetic susceptibility data for this compound indicated a spin-glass-like behavior below T-g = 3.7 K, which is attributed to disturbance of the antiferromagnetic superexchange interaction by the B-site deficiencies.