The aim of the study was to evaluate of Festuca arundinacea Schreb. spec. Rahela (Tall fescue) and Spartina pectinata L. suitability for biogas production. Biomass of investigated C3 and C4 grasses was grown in Experimental Station of Warsaw University of Life Sciences in Skierniewice, harvested on the 30th of June 2014 and ensilaged. Methane fermentation of experimental silages was carried out under mesophilic conditions (39°C) for at least 21 days. Fresh biomass of spartina contained higher amount of volatile solids, crude fiber and higher ratio of C/N compared to fescue biomass. Both grasses were susceptible to ensiling. Obtained silages were in good quality, secondary fermentation process was not detected. Silages from spartina contained much higher amount of acetic acid than lactic acid. After methane fermentation of silages prepared from spartina and fescue 734,1 ± 34,33 m3 · t-1dm and 722,7 ± 52,52 m3 · t-1dm of biogas with 55% of methane content was obtained respectively and differences were not significant (p >0,05). Taking into account higher biomass yield of spartina than fescue, examined C4 grass seems to be more suitable alternative source for biomethane production.