The production of extracellular cellulases by Penicillium citrinum, on agriculture waste materials was studied in solid-state fermentation (SSF). The objective of this research is to study on optimal conditions for cellulase production by Penicillium citrinum. The study determined a different concentration raw materials of culture conditions such as carbon and nitrogen source, moisture content, duration, citrate buffer extraction. Cellulase activity was determined by measuring the absorbance χ = 540 nm with 3, 5 – DNS reagent. In the optimal culture conditions, cellulase activity of Penicillium citrinum obtained 87.83 U/mL in enzyme activity. The results showed that the high-level cellulase activity was produced at 40% rice husk, 59% rice bran, 1% urea and 60% moisture content, in 4 days with 70mL citrate buffer for extraction. Thus, the enzyme activity would be increased by purification.