Microalgae has gained immense interests as the raw material for biofuel production. The lipid content in microalgae can be converted into biodiesel through conventional method which involves separated process of extraction and transesterification. In this study, the production of biodiesel from Spirulina sp. was performed through one-step extraction-transesterification using KOH as base catalyst to simplify the production of biodiesel. The mixture of methanol-hexane was employed as both solvent and reactant in the process. The resulting biodiesel was found to be mainly composed of methyl oleate and methyl palmitate. On the other hand, increasing the reaction temperature and reducing the quantity of methanol in solvent mixture would also increase the yield of biodiesel. The optimum methanol-hexane volumetric ratio and temperature which gave the highest biodiesel yield were 3:7 and 50°C, respectively.