Direct extraction and conversion of microalgal lipid to biodiesel in one step process is developed to initiate an efficiently method in the biofuel production. The method that called as in-situ process had been applied in the biodiesel production from microalgae Chlorella vulgaris lipid by involving of sonication assisting. Various parameters that affect the in-situ transesterification were investigated to find the optimum conditions including power of sonication, co-solvent use, and biomass amount. The experiment was performed by acidic catalyst The use of sonication in 25kHz/270W yielded the highest biodiesel product. The apply of co-solvent n-hexane significantly increased the yield biodiesel rather than no co-solvent. The biodiesel yield of 10.39 % obtained when the process was accompanied by the n-hexane.as co-solvent with increasing level as 47% rather than without co-solvent. The in situ process in the ratio biomass - methanol 3:50 that assisted by sonication for 60 mins produced the highest biodiesel, which was 20,31 % w/w. The yield was higher than assisting with reflux or combination of reflux-sonication. The component of biodiesel yielded in the process consisting of 7,10,13-hexadecatrienoic methyl ester; pentadecanoic acid, 14-methyl-methyl ester; 9,12,15-octadecatrienoic acid-methyl ester; and eicosanoic acid-methyl ester. Joining of reflux-sonication exhibited a low biodiesel product. Disadvantage method from the combination may inhibit on lipid extraction or FAME transformation, the exact cause needs to be looked for in the future.
 
 Keywords : Biodiesel, in-situ transesterification, microalgae Chlorella vulgaris, sonication