Waste banana stem has a high organic content (83%); with 15-20% (w/w) lignin and cellulose which gives it a sheath-like texture. Banana stem slurries (BSS) at 2-16% total solids (TS) concentration were anaerobically digested under mesophilic (37-40 degrees C) as well as thermophilic conditions (50-55 degrees C) in batch culture. The final biogas yields, 267-271 l/kg TS fed, were observed with 2-4% TS slurries, under mesophilic conditions. In the thermophilic range, the biogas yields, 212-229 l/kg TS fed, were found with 2-8% TS slurries. However, thermophilic digestion rates were 2.4 times faster than mesophilic. Methane accounted for 59-79% of the total biogas. Methane yield was maximum at 2% TS BSS in both the temperature ranges. The process led to 45-50% reduction in organic solids and 40-55% reduction in COD. With 16% TS BSS inhibition resulted in 50-60% loss in biomethanation process efficiency.