Abstract: Mannanase is an enzyme which is capable of breaking down mannan substrate by hydrolyzing the β-1.4-manosidic linkage between mannose and mannose. Mannanase can be applied to feed, paper, pharmaceutical, food, detergent, oil and gas industries. In the pharmaceutical industry, mannanase can be used for controlling drug release from composed matrix from cross-linked galactomannansThe objective of this study is to discover the activity of the bacterium Bacillus subtilis ATCC 6633 in producing mannanase through a fermentation process using PKC mediumThis kind of research is true experimental research with replications.The research results recommend to increase the utilization of palm kernel cake (PKC) as a medium and Bacillus subtilis ATCC 6633 as a source of mannanase, after production optimization, either in laboratory, pilot or commercial scale, by changing various factors which affect the productivity of Bacillus subtilis ATCC 6633 to determine the optimal time of fermentation, so that the result produces maximum mannanase activity.Bacillus subtilis ATCC 6633 is capable of producing mannanase through the fermentation process using PKC as a medium. Furthermore, the mannanase Bacillus subtilis fermented result activity ATCC 6633 was using 0.25% of PKC as a medium produced a mannanolytic index of 4.0 ± 0.98.