Effects of media composition, and physical properties on the production of crude mannanase by Penicillium oxalicum KUB-SN2-1 were investigated. P.oxalicum KUB-SN2-1 was propagated in a shaking incubator at 30°C with rotation speed of 200 rpm of 7 days. The specific activity obtained during growth on robusta coffee residues (RCR) of 16.21 U/mg protein was much higher than other carbon sources tested. For nitrogen sources, yeast extract (0.11 U/mg protein) and ammonium nitrate (0.09 U/mg protein) showed maximum specific activity. Hence, guar gum was the best inducer for producing mannanase (14 U/mg protein). For evaluating the optimal concentration, the result showed that 1% guar gum, 0.5% yeast extract, 0.25% ammonium nitrate, and 0.25% RCR were the suitable sources of inducer, organic nitrogen, inorganic nitrogen, and carbon, respectively. Modified medium with initial culture pH of 5.0 at 30°C was optimum for mannanase production (53.77 U/ml for 3 day). Reducing sugars were analyzed by dinitrosalicylic acid methods. The highest reducing sugar of 7517.82 μg/ml was obtained from copra meal hydrolysate after 30 h.