Several clean development mechanism projects for bioenergy production have been started in Southeast Asia. However, the effect of these projects on the lifecycle aspect of biomass production is still unclear. This study aimed to evaluate GHG emission of tapioca starch production and the GHG reduction potential of biogas utilization through field investigation in Lampung province, Indonesia. GHG emission was calculated by considering biomass carbon balance, fossil fuel and chemical fertilizer consumption, nitrous oxide emission and methane emission. First, we estimated the biomass carbon balance of tapioca production. The results showed that 42% of cassava carbon was converted to tapioca starch and 16% to wastewater and other for biomass residues. In addition, 34% of wastewater carbon was converted to methane in wastewater treatment pond. Based on these results, this study clarified that GHG emission of tapioca starch production was 1.4 t-CO(2)eq/t-tapioca. GHG of methane from wastewater treatment accounted for 63% of total GHG emission. Therefore, this study considered GHG reduction by biogas utilization. The results showed that 64% of GHG emission will be cut by biogas utilization, and that GHG emission will be reduced by 0.49 t-CO(2)eq/t-tapioca.