Providing the optimal temperature is a means of increasing the effectiveness of methane fermentation processes. The use of an electromagnetic microwave field enables energy to be directed to a mixture of anaerobic sludge and processed biomass this reduces energy losses. The aim of this study was to determine the effect of electromagnetic microwave radiation in stimulating thermal conditions in anaerobic reactors, on the effectiveness of methane fermentation process of microalgae biomass and on the qualitative composition of biogas produced. The quantity of gaseous metabolites of anaerobic bacteria produced in both experimental variants (convective and microwave heating) averaged approximat’s 450 cm³ g⁻¹ VS. The electromagnetic microwave radiation proved to have an immediate impact on the improvement in the qualitative composition of biogas produced. The stimulation of thermal conditions using electric heaters resulted in a methane contetnt of 65% in biogas, whereas the use of microwaves assured ca. 69% in sewage gas.