Cellulases are enzyme complex of hydrolytic enzymes such as endoglucanase (CMCase), exoglucanase, ß-glucosidase (BGL) and FPase that are responsible for the bioconversion of the cellulosic biomass into valuable products. Aspergillus niger were isolated from the waste of rice field and grown on potato dextrose agar medium. Morphological studies were done on different pH, incubation period and different concentration of ammonium sulphate. pH 7.7, 72 hrs of incubation and 0.14% ammonium sulphate were most suitable for the growth of Aspergillus niger. Plate screening was done by using carboxy methyl cellulose as carbon source which showed clear zone formation on staining with congo red dye. By using DNSA method, cellulase activity was observed at different nitrogen source with different concentration, pH and incubation time. pH 4.2, 96 hrs incubation period, 0.125% peptone, 0.14% ammoniumsulphate and 0.04% urea were best for cellulase activity.