Cu2ZnSnS4 (CZTS) nanoparticle inks were synthesized for the first time by a one-pot synthesis method using microwave heating. Precursor solutions were mixed and reacted at 190 °C for 30 min. Varying the initial concentration of the metal chlorides in ethylene glycol was necessary to avoid formation of copper rich and zinc poor nanoparticles. Analysis of the reaction supernatant indicates that Cu+ was fully utilized while significant amounts of Zn2+ remained unreacted. The CZTS nanoparticles were determined to be 7.6 ± 2.1 nm in diameter and were found to agglomerate into larger clusters. A solar cell fabricated with the CZTS nanoparticles had a conversion efficiency of 0.25%.