The effect of agitation speed and incubation period on the production of mannanase enzyme by Bacillus velezensis NRC-1 using bench-scale bioreactor at 45ºC was investigated. Results revealed that the increase in agitation speed from 200 to 800 rpm resulted in a significant increase in mannanase production to 21.04 U/mL. The increase in agitation speed affected dissolved oxygen (DO) concentration which in turn affected cell growth and mannanase production. The maximum mannanase production in the bioreactor was attained after 72 h of incubation at 45 ºC.  Mannanase activity in the bioreactor (21.04 U/mL) while much higher than that obtained from the shake flask fermentation (15.6 U/mL) also the incubation period decreased from 7 days in shake flask fermentation to 3 days in bioreactor.