The partial disruption of tea leaves during processing of tea in conventional methods reduces the amount of peroxidase and polyphenoloxidase in the native leaves. Exogenously addition of natural cellulolytic enzymes may improve the quality of black tea produced. Due to their high cost, enzyme addition has not received many attentions in our area. In this research, cellulase was extracted from symbiotic tea fungies in order to study its effect on improvement of tea quality. The extracted cellulase is in fact a cellulolytic enzyme system containing endo- and exo-glucanase, cellobiohydrolase and cellobiase. The enzyme system was partially purified and the optimum pH and temperature as well as the kinetic parameters (K-m and V-max) calculated. The efficiency of the partially purified enzymes was then investigated in the other part of research where the tea processed with the extracted enzymes was compared with the tea samples processed in conventional methods. It was shown there that the partially purified enzyme extracts were highly effective in improving the quality of Iranian tea in terms of total liquor color, total soluble solids, and caffeine and dry matter. (c) 2005 Published by Elsevier Inc.