Background and objectives: Turbidity is a desirable property in some juices such as carrotkiwi juice that is influenced by the presence of released pectin. Pectin methylesterase (PME) causes turbidity loss in the juice because of desterification of the pectin. THERMAL processing is the most common method to PME INACTIVATION. The aim of this study was investigation of PME INACTIVATION during THERMAL processing of carrot-kiwi juice at different temperature. Materials and methods: To study the PME INACTIVATION, the carrot-kiwi juice was heated at 60, 70, 80 and 90 ℃ at different time (proportional to the temperature). D and Z-value and THERMAL dependence kinetic parameters consisting of activation energy (Ea), enthalpy (Δ H), entropy (Δ S) and free energy (Δ G) of the THERMAL INACTIVATION of PME were calculated. Results: Based on the obtained results, the Z-values of heat sensitive and heat resistant isoforms of PME in the juice during processing at 60, 70, 80 and 90 ° C were calculeted 17. 85 ° C and 22. 27 ° C, respectively. The required Ea to inactivate the heat sensitive and heat resistant isoforms of PME in the carrot-kiwi juice were 356. 83 kJ/mol and 257. 17 kJ/mol, respectively. Also, enthalpy for INACTIVATION of the heat sensitive and heat resistant isoforms ranged between 354. 1 to 353. 8 kJ. mol-1 and 254. 4 to 254. 1 kJ. mol-1, respectively. During the juice THERMAL processing, the entropy of the INACTIVATION of the heat sensitive and heat resistant isoforms were calculated 0. 79 to 0. 73 K-1. kJ. mol-1 and 0. 47 to 0. 43 K-1. kJ. mol-1, respectively. The free energy related to the INACTIVATION of the heat sensitive (91. 1 to 87. 3 kJ. mol-1) and heat resistant (97. 9 to 97. 0 kJ. mol-1) isoforms of PME were measured. These results represent the effect of temperature on the protein structure of the PME. In addition, the effectiveness percentage of the come up time (CUT) on INACTIVATION of the heat sensitive and heat resistant isoforms of PME in the carrot-kiwi juice were computed. Conclusion: By considering the effect of come up time and THERMAL resistance of the heat sensitive isoform of PME, the required pasteurization time for carrot-kiwi juice at 75, 80, 85, 90 and 95 ℃ were 22. 14, 11. 61, 6. 09, 3. 19 and 2. 01 min, respectively.