The electronic and optical properties of Cu2ZnSnX4 (X = S, Se) have been studied using the highly accurate Tran-Blaha-modified Beck and Johnson (TB-mBJ) potential. From this study, it has been found that these compounds are direct band semiconductors and the value of band gap increases from Se to S. The values of the band gap, density of states, bulk modulus, dielectric functions, real part of optical conductivity, and absorption coefficient are reported. The calculated band gap value is found to be in excellent agreement with the recent experimental results. A comparison of the calculated properties with available experimental data indicates that the TB-mBJ approach provides a better description of the electronic and optical properties of the compound than the standard GGA approaches.