Abstract Biogas plant (BGP) with anaerobic digestion is receiving high attention as a facility for both livestock manure treatment and electric power generation. The objective of the study was to compare an on-farm BGP with a centralized BGP system totally from the energetic point of view. The basic data for this evaluation were obtained from the centralized BGP in Betsukai, Hokkaido, which was built on May 2001 for the experimental purpose by the Civil Engineering Research Institute of Hokkaido. We used two evaluation methods. First, to estimate how global warming gas is influenced by BGP systems, we used life cycle assessment (LCA). Estimated emission of CO 2 was about 2700 t from the introduction of BGP. The production of CO 2 at the time of biogas combustion (1080 t) was not included in emission because of the concept of carbon neutral.