The quaternary compound Cu_2ZnSnS_4 (CZTS) single crystals were successfully grown by Traveling Heater Method (THM). We determined that suitable THM growth conditions for CZTS single crystals are a Sn solution with X = 70 mol% and growth temperature of 900˚C, on the basis of the CZTS-Sn pseudobinary phase diagram. Temperature dependent Hall effect measurements from 20 to 300 K have been performed on CZTS single crystals. The conductivity mechanisms can be described by a two-path system using Mott variable range hopping and typical thermal activation conduction. The center level of the acceptor band is 132 meV above the valence band maximum and is of width 40 meV. A correlation between the activation energy and acceptor concentration in CZTS is observed.