Abstract: The pectin in tobacco stem negatively affects the sensory quality of cigarette. In order to reduce the pectin content in stems, a pectinase applicable to degrading pectin in stems was screened from four acidic pectinases. The effects of processing factors on pectin degradation rate, including the applying rate of enzyme, stem/liquid ratio, pH, processing time and temperature were investigated by single factor experiments. The optimal processing conditions gained by means of orthogonal test were:enzyme rate 100 U/g, stem/solution ratio 1:20, initial pH 3.0, reacting for 8 hours at 45℃. The maximum degradation rate reached 42.38% under the optimal conditions.