Polarization-dependent electrolyte electroreflectance (EER) measurements were carried out on the oriented Cu 2 ZnSiS 4 and Cu 2 ZnSiSe 4 single crystals at room temperature. Thin blade single crystals of Cu 2 ZnSiS 4 and Cu 2 ZnSiSe 4 were grown by chemical vapor transport technique using iodine as a transport agent. Laue pattern normal to the basal plane of the as-grown crystal revealed the formation of orthorhombic structure with the normal along [210] and the c axis parallel to the long edge of the crystal platelet. The polarized EER spectra in the vicinity of the direct band edge of Cu 2 ZnSiS 4 displayed distinct structures associated with transitions from two upper-most valence bands to the conduction band minimum at Γ point. In the E⊥c configuration, the feature designated as E A ∼3.345eV was detected and for Е‖c, only E B ∼3.432eV appeared. For Cu 2 ZnSiSe 4 , three features denoted as E A , E B , and E C at around 2.348, 2.406 and 2.605eV, respectively, were recorded for E⊥c polarization, whereas in the Е‖c, only E B and E C were the allowed transitions. Based on the experimental observations and a recent band-structure calculation by Chen et al. [Phys. Rev. B 82 (2010) 195203], plausible band structures near the direct band edge of Cu 2 ZnSiS 4 and Cu 2 ZnSiSe 4 have been proposed.