This study has been conducted to do life cycle environmental impact assessment for cement –mortar brick household bio-digester and reinforced fiberglass household bio-digester. Primary and secondary data are used for the work. Data analysis was made using openLCA version 1.8 software and impact assessment method selected is CML (baseline) with normalization and weighting to global, 2000. Detail analysis made using graph and table by exporting LCIA result to excel. The functional unit is ‘generation of 1GJ energy from each 6m3 bio-digesters at anaerobic condition and the produced biogas energy is used for cooking and lighting for household. The study is from cradle to grave and the life span of both bio-digesters is considered 20 years. According to life cycle assessment for biogas, system boundary is confined to bio-digester construction, operation and maintenance and end of life disposal. Allocation is made for bio-slurry produced as a co-product for substituting chemical fertilizer. The result of the study indicated that cement mortar brick bio-digester construction consumed more energy than it able to produce in its life span operation with energy pay back ratio of 0.25 and energy payback time of about 80 years. However, fiberglass reinforced bio-digester has higher energy payback ratio of 3.2 and energy payback time of 6 years. Total emission caused by cement mortar brick bio-digester is 122.64 tons CO2e and the share of raw materials extraction, processing and construction is 95.9 % and that of operation and use is 4.1%. On the other hand amount of emission saved by this bio-digester in its life span is estimated to 323 tons CO2e making net emission reduction of 200.4 tons CO2e. For fiberglass reinforced bio-digester, total emission was 1349 tons CO2e and the share of raw materials extraction, processing and construction of the bio-digester is 99.6 % and that of operation and use is 0.4 %. Emission reduced by this bio-digester was 323 tons CO2e making the digester affecting the environment with 1026 tons CO2e emission. Bio-slurry use, energy change and fuel saved contributed 11.4%, 66.3% and 22.3% for the emission reduction respectively. The study also indicated that upstream and direct process contribution to the impact for cement mortar brick bio-digester construction is on average 61% and 39 % respectively whereas 63.4 % and 36.6 % for fiberglass reinforced bio-digester.