Pectolytic enzymes, viz., polymethylgalacturonase (PMG), polygalacturonase (PG), and pectinlyase (PL) were deactivated at various combinations of pH and temperature. The deactivation process was modelled as first-order kinetics and the deactivation rate constant was found to be minimum at pH 2.2 and 23 °C, respectively for PMG, 4.8 and 28 °C, respectively for PG and 3.9 and 29 °C, respectively for PL. Thermodynamic parameters like ΔG*, ΔH*, ΔS*, and activation energies were evaluated for crude and partially purified enzymes. It was found that entropy values are negative for all the three enzymes. The partially purified enzymes were found to be less stable than the crude enzymes. Hence, the interaction effect among the enzymes and also the effect of protein (BSA) on deactivation were studied. The addition of protein doubled the half-life times of partially purified PMG, PG I and PG II. The interaction effect of pectolytic enzymes on deactivation was found to be significant. © 2003 Elsevier Science B.V. All rights reserved.