Abstract: Eleven isolates of thermophilic bacteria were isolated from hot spring and collected from West Sumatera of Indonesia. The bacteri isolated were grown on medium agar containing locust bean gum at 60°C for 48 hours to examine their mannanase production by using Congo red test. It was found that four isolates showed positive results with clear zone around the cultures. All isolates were evaluated their mannanase activity by growing in liquid medium supplemented with 0.5% locust bean gum as mannan source. It was found that isolate SM-1.4 displayed that highest enzyme activity of 119,44 U/ml and specific activity of 19.55 U/mg protein. The optimal growth conditions were at 60°C, pH 7 and 24 hours of incubation. According to the morphological studies, the isolate SM-1.4 was primarily identified as the genus Bacillus. The bacteria was gram negative and has endospore.