In this study, biodiesel was produced from microalgae (Chlorelia) through a one-step process that involves simultaneous lipid extraction and transesterification under ultrasonic irradiation in the presence of CaO as the alkaline solid catalyst. The effect of ultrasonic irradiation with and without additional solid particles (alumina) on the simultaneous process was investigated. The variation of three parameters was evaluated: ultrasonic power (60-360W), catalyst concentration (3-12 wt%), and reaction time (15-60 min). Then, the effect of alumina particles on biodiesel conversion was assessed by analysis with the conventional two-step process (lipid extraction followed by transesterification). The addition of alumina particles had a remarkable effect on the transesterification and only a slight impact on the lipid extraction step.