Anaerobic digestion of corn silage was studied in a semi-continuous anaerobic plug flow reactor (PFR) at mesophilic condition. This work study the influence of increase in organic loading rate (OLR) on biogas production and other important parameters during anaerobic digestion. Varied OLR in the range of 3.5-8.5 kg M-3 d(-1) (volatile solids (VS) fed basis)-volatile fatty acids (VFA) and FOS/TAC value increased with OLR, was stable up to 6.5 kg M-3 d(-1), and became critically unstable when OLR was 8.5 kg m(-3) d(-1). An increase in biogas production was perceived with each upsurge in OLR, although CH4 concentration decreased and H2S content increased under high loading. The PFR lost its stability at 8.5 kg M-3 d(-1) OLR that was apparently observed by decline in biogas yield and CH4 content.