The stereochemically active lone pair (SCALP) effect of Pb2+ plays a vital role in enhancing the nonlinear optical response and engineering the band gap of lead-based materials with intriguing properties. Herein, we combined SCALP Pb2+ cations and π-conjugated (HC3N3O3)2- anions into one structure to investigate the tunable optical properties. Two lead cyanurates, namely, Pb3(HC3N3O3)2(OH)2 (I) and its partly cadmium-substituted analog Pb2Cd(HC3N3O3)2(OH)2 (II) were grown by the mild hydrothermal method. They exhibited greatly narrowed bandgaps and enhanced optical anisotropy resulting from the SCALP effect. In addition, divergent optical responses induced from the involved Pb (6s26p2) and Cd (4d105s2) were elaborated by a combination of experimental and theoretical analyses.