This work embarks on finding an efficient method to synthesize biodiesel from wet microalgae. In this study, a benzimidazolium based Brønsted acid ionic liquid catalyst (BBAIL) is used for the conversion of microalgae with the aid-in of ultrasonication, for the first time. The optimum biodiesel yield i.e. 58.35 wt.%, is obtained using methyl alcohol (MA) to oil molar ratio 570:1, 12.6 wt.% catalyst loading, 63 min. reaction time and 455 W ultrasonication power. Also, the reaction kinetics and thermodynamics of in-situ transesterification of wet algae 'Scenedesmus sp. ASK22' is presented. The lower value of activation energy and higher value of kinetic constant indicate the fast rate of reaction, which could be attributed microturbulence generated due to ultrasonication. The positive values of Gibbs-free energy (ΔG), the negative value of entropy (ΔS) and the positive values of enthalpy (ΔH) indicate that the reaction is non-spontaneous, endergonic and endothermic, respectively. [ABSTRACT FROM AUTHOR]