In-situ transesterification of wet microalgae is one of the emerging methods to produce biodiesel as this approach exclude energy-intensive steps (e.g. drying and lipid extraction) through process merging. Nevertheless, studies related to reaction kinetics and thermodynamic of such process are still limited in the literature while this information are necessary for process design and intensification. Thus, the present study was aimed to evaluate the reaction kinetics and thermodynamics of in-situ transesterification of wet Chlorella vulgaris. It was found that the fatty acid esters (FAE) yield was increased with reaction time and temperature due to gradual conversion of esterifiable lipids to FAE and higher kinetic energy of reactants. In-situ transesterification of C. vulgaris at 60 °C resulted high FAE yields (>90 wt.) within a short reaction duration (25�35 min). The in-situ transesterification of C. vulgaris was found to follow first order of overall reaction (with respect to esterifiable lipids) and attained activation energy (EA) of 50.4�60.4 kJ/mol. In addition, the in-situ transesterification of wet C. vulgaris is an endothermic (�H = 50.4�60.4 kJ/mol) and non-spontaneous (�G = 87.7�88.4 kJ/mol) reaction that decreased the randomness of reaction system (�S = �0.082 to �0.114 kJ/mol K). © 2021 Institution of Chemical Engineers