The aim of this study was to determine the optimum conditions of the biodiesel production from refined and unrefined olive pomace oil. The refined olive pomace oil had an acid value of 2.34 mg KOH / g-oil. Therefore, transesterification reaction could be directly applicable due to the low free fatty acids content. To improve the yield of the transesterification reaction, some parameters were optimized: the catalyst and solvent concentration, the temperature and the reaction time. The biodiesel yield reached 100% with the following combination: 15: 100 ml (v/v) methanol to oil volume ratio, 1g of potassium hydroxide, at 50 °C during 60 min. The stirring rate was maintained constant (400 rpm). The unrefined olive pomace oil had an acid value of 44 mg KOH / g-oil. Due to its high free fatty acids content, a pretreatment step, an esterification reaction, was required to decrease the percentage of free fatty acids to the limit allowing the realization of the transesterification reaction. The optimum conditions of the pretreatment process which provided the lowest acid value were as follows, 65:100ml (v/v) methanol and 1.25 ml of sulfuric acid to oil volume ratio, at 50°C during 60 min and at a stirring rate of 400 rpm. Conditions already optimized with the refined olive pomace oil for the transesterification process were preserved for the pretreated one. The yield of the produced biodiesel in that case reached 99 %.