Fusion synthesis of Ca-resinates was studied in a laboratory reactor and in a thermobalance. In the syntheses, the resination reaction takes place at 235 degreesC and it is followed by the thermal decarboxylation of rosin acids at 265 degreesC. The kinetics of the thermal decarboxylation was modelled in the synthesis reactor using calcium contents corresponding to the theoretical target acid values 50 to 90 mg(KOH)/g. In the thermobalance, the kinetics of the decarboxylation reaction could be continuously followed and accurate kinetic results were thus obtained in different reaction conditions. The oxidative and thermal decarboxylation were separately studied in the thermobalance at the reaction temperature range of 245 degreesC to 275 degreesC and in different atmospheres (air, N-2, CO2) at 260 degreesC. The oxidative decarboxylation was observed to be faster than the thermal decarboxylation during the first 2 h. After that, however, the oxidative decarboxylation was restricted by the apparent reaction equilibrium.