The use of ruminal fluid as a source of hydrolytic microorganisms for the pretreatment of a native consortium of microalgae (essentially Senedesmus) was investigated. The hydrolytic enzyme activity of the ruminal culture was first enriched in a bioreactor. Then, using the enriched culture, the effect of the microalgae to the ruminal fluid ratio (S/X) on the hydrolysis and subsequent production of methane was investigated. An S/X ratio of 0.5 showed the best hydrolysis efficiency (29%) reaching in a second stage process a methane yield of 193 mL CH4 g COD-1. The processing time (pretreatment plus methanization) was only 7 days. The predominant ruminal hydrolytic bacteria selected in the enrichment were principally Clostridium, Proteocatella and Pseudomonas.