To calculate life cycle energy (LCE) of sewer systems like conventional gravity system only, alternative gravity system with pumping stations, pressure system and vacuum system, unit energy values of materials were referred from papers but energy consumption of producing process were collected from many factories in Japan. Construction energy was calculated based on standards of cost estimation. Operation and Maintenance energy of pressure/vacuum systems were estimated based on the investigation by interviewing and questionnaire. Energy saved alternatives were considered in each sewer system and 11 alternatives were compared in the condition of 20 ha area, 70 persons/ha, flat and 2m ground water level from surface by LCE converted into annaual value and annual change in case study.