Concurrent enhancement of hydrolysis efficiency (30 %) of C. vulgaris biomass and the improvement of biogas production (1.9-fold) by applying Fe3O4 NPs pretreatment prior anaerobic digestion were the main finding of the current study. Proper NPs concentration (10 ppm), pretreatment time (40 min) and biomass load (16 g/L) led to elevated organic matter solublization and maximum biogas yield enhancement. The effectiveness of hydrolysis and improvement of biogas production were both declined when biomass load was increased. Current study outcomes indicate a possible new strategy for NPs design prior microalgae anaerobic digestion for weaking its robust cell wall and subsequent process optimization.