This study investigated the impact of compaction on anaerobic degradation of municipal solid waste (MSW) during the phase of decelerated methane formation. Two stainless steel lysimeters were constructed by equipping a hydraulic cylinder to apply pressure load on the MSW. When methane production rates decreased from the peak rate of each column, pressure load was applied at different degrees of decomposition (DOD). Methane production rate increased when compaction was applied. However, the impact of compaction on the methane production rate varied according to DOD. The MSW compaction reduced MSW pore space, increasing the contact surface area among MSW lumps. It was hypothesized that the mass transfer of substrate and substrate accessibility could be enhanced due to the decrease of void space and the increase of the contact area among waste mass as a consequence of the compaction. (C) 2015 Elsevier Ltd. All rights reserved.