This study addresses in situ transesterification of highly saturated wet microalgae with hydrochlo-ric acid (HCl) as a catalyst. In situ transesterification was performed by heating the mixture of wet algal cells, HCl, methanol, and solvent in a single pot, resulting in the fatty acid methyl ester (FAME) yield over 90 wt. % at $95^\circ C$. The reaction variables including temperature, amounts of catalyst, reactant, and solvent, and type of solvents were investigated. Compared with the catalyt-ic effect of sulfuric acid, in situ transesterification using HCl has benefits of being less affected by moisture levels that are as high as or above 80 wt. %, and requiring less amounts of catalyst and solvent. For an equimolar amount of catalyst, HCl showed 15 wt. % higher FAME yield than sul-furic acid. This in situ transesterification using HCl as a catalyst would help to realize a feasible way to produce biodiesel from wet microalgae.