This study investigated the improvement of biogas production from solid-state anaerobic digestion (SS-AD) of oil palm biomass by optimizing of total solids (TS) contents, feedstock to inoculum (F:I) ratios and carbon to nitrogen (C:N) ratios. Highest methane yield from EFB, OPF and OPT of 358, 280 and 324 m(3) CH4 ton(-1) VS, respectively, was achieved at TS content of 16%, C:N ratio of 30:1 and F:I ratio of 2:1. The main contribution to methane from biomass was the degradation of cellulose and hemicellulose. The highest methane production of 72 m(3) CH4 ton(-1) biomass was achieved from EFB. Bacteria community structure in SS-AD process of oil palm biomass was dominated by Ruminococcus sp. and Clostridium sp., while archaea community was dominated by Methanoculleus sp. Oil palm biomass has great potential for methane production via SS-AD. (C) 2016 Elsevier Ltd. All rights reserved.