The purpose of this study was to produce a higher amount of cellulase by using an alternative carbon source, such as banana agrowaste, and to optimize the fermentation parameters for a high yield. In the present study, cellulase-producing Penicillium was isolated from a decaying wood sample. Different nutritional and environmental factors were investigated to assess their effect on cellulase production. The highest crude enzyme production was observed at a pH 6.0 and a temperature of 28°C in a medium that was supplemented with banana agrowaste as the carbon source. Pretreatment with 2N NaOH, at 7% substrate (banana agrowaste) concentration yielded the highest cellulase activity. Further to this, the effect of other parameters such as inoculum age, inoculum size, static and agitated conditions were also studied. It is concluded that Penicillium oxalicum is a powerful cellulase-producer strain under our tested experimental conditions using banana agrowaste as the carbon source.