The kinetics of commercial pectinase, Pectinex Ultra SP-L, in a batch reactor was studied. The change in viscosity of pectin solution was followed by an enzymatic assay to determine pectolytic activity of the enzyme preparation. The pectolytic activity of Pectinex Ultra SP-L was measured at pH 3.5 and 35 degrees C and found to be 0.025 pectin % (w/v)/sec/enzyme % (v/v). The Michaelis-Menten constant (K-m) of enzyme preparation was found to be 1.137 pectin % (w/v). The temperature dependence of the reaction rate was obeying the Arrhenius Law. The activation energy of the biochemical reaction catalysed by commercial pectinase was calculated as 9.316 kcal mol(-1).