The kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) were successfully synthesized using a relatively simple and one-step hydrothermal route. The structural, compositional, and optical properties of the kesterite CZTS NCs have been studied in detail. The pH-dependent CZTS phase formation has been elucidated for the first time. The X-ray diffraction and Raman spectroscopy confirmed the formation of a main phase kesterite CZTS structure only at pH 7. However, for pH values (4.3, 5, and 9), the formation of CZTS alongwith few secondary phases like Cu2SnS3 (CTS), Cu2−xS, and SnS2/Sn2S3 have been detected. CZTS NCs of size 10–100 nm were obtained at 200 °C and pH 7. The synthesized NCs showed a pH-dependent variation in optical band gap values from 1.15 to 1.44 eV, which is near optimum value for low cost thin film solar cells.