The utilization of nonlinear optical (NLO) crystals plays a crucial role in the contemporary laser industry, and the advancement of novel NLO-active units is essential for the exploration of NLO materials. Two novel organic-inorganic hybrid iodates, designated as (C3N2H5)2Mo2O5(IO3)4·3H2O (1) and (C3N2I2H3)2Mo2O5(IO3)4·4H2O (2) were synthesized via mild hydrothermal methods, exhibiting band gaps of 3.75 and 3.00 eV, SHG response of 1.3 and 3.5 times that of KDP, and birefringence of 0.143 and 0.254@ 550 nm, respectively. The optical property enhancement can be attributed to the cationic modification strategy, as corroborated by the results of theoretical calculations.