Recombinant $eta$-glucosidase from Thermus caldophilus GK24 was easily purified partially by a heat treatment procedure, resulting in 8-fold and recovery yield of 80% from crude enzyme. When the $eta$-glucosidase was incubated with a 80% glucose solution (w/w), gentiobiose ($eta$1,6-glucobiose) was the major product in the reaction mixture. The optimal conditions for producing gentiobiose (11% yields of total sugar) were pH 8-9 and 7$0^{circ}C$ for 72 h.