Cu2ZnSnS4 (CZTS) nanocrystals (NCs), a promising alternative for In- and Ga-free absorber materials, were snythesized by a novel route using a two-step process. In the first step, the precursor powders were obtained by microwave irradiation at 700 W for 10 min from aqueous solutions containing copper, zinc, tin and sulfur elements. In the second step, the precursor powder was sulfurized by annealing in H2S (5%) + N2 (95%) atmosphere at 550 °C for 1 h. The structural, compositional, thermal and optical characteristics of CZTS NCs have been investigated. X-ray diffraction patterns, X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the sulfurized NCs were a single kieserite CZTS phase without Cu2SnS3, ZnS, CuS and SnS secondary phases. Thermo-gravimetric analysis and differential-thermal analysis indicated a weight loss at about 840 °C and endothermic peak at same temperature from CZTS nature. Energy dispersive X-ray results showed that composition of CZTS NCs had a Cu and Zn-rich and S-poor. UV–vis spectroscopy results indicated that the absorption coefficient was over 104 cm−1 in the visible region. The direct band gap energy of the CZTS NCs estimated at about 1.5 eV, is ideal for its use in photovoltaic applications.