We have synthesized Cu2ZnSnS4 (CZTS) sintered compacts with different compositions and investigated their transport properties to understand effects of nonstoichiometry and defects. The synthesized Cu2ZnSnS4, whose nominal molar ratios were stoichiometric, was a p-type semiconductor and had a low carrier mobility of 0.09 cm2/Vs with a carrier concentration of 5 × 1018/cm3 at room temperature. The carrier mobility increased by lowering the carrier concentration when the Zn or Sn content of CZTS increased. It probably originates in reducing antisite defects at Zn and/or Sn site, which generate hole carriers and scattering centers of carriers.