Effects of carbon sources, incubation time, incubation temperature, initial incubation pH, and vitamin B complex on the polygalacturonase activity of Byssochlamys fulva were studied to confirm the optimum conditions for the production of that enzyme. When pectin was used as carbon source, polygalacturonase activity reached to the maximum value of 0.50 units/ml. After 5 days of incubation, polygalacuturonase activity reached to its maximum of 0.48units/ml. Polygalacturonase activities were similar between $25^{circ}C;and;45^{circ}C$, however, decreased dramatically in the outside of this range. Polygalacturonase activity was not signicicantly influenced by the variation of initial incubation pH. However, at pH5.0, polygalacturonase activity was slightly through the addition of thiamine and riboflavin, and the optimum concentrations were $10^{-2}M$ in case of thiamine and $10^{-3}M$ in riboflavin.