The present study reports the synthesis of colloidal Cu2ZnSnS4 (CZTS) nanocrystals (average size ~4–9 nm) by a simple and low cost hot-injection method. These nanocrystals form larger particles with sizes around 40 nm. Oleylamine (OLA) was used as both the solvent and the nanocrystal stabilizer. The effect of the synthesis time on the structural, compositional, morphological, and optical properties was studied. As revealed by XRD, Raman, and TEM measurements all the prepared samples are comprised of both kesterite and wurtzite CZTS nanocrystals. The wurtzite phase contribution reduces as the reaction time is increased. The “bandgap” of the obtained nanoparticles tends to 1.52 eV for the larger synthesis times (24 h) which is suitable for an absorber layer in thin films solar cells.