Results of life cycle inventory (LCI) and life cycle assessment (LCA) for septic tanks collecting domestic sewage were presented. The study included the whole life cycle: construction, use and end-of-life stages of septic tanks. The analyses were conducted basing on actual data concerning performance of 793 septic tanks in Żory. Environmental impact assessment of the life cycle of septic tanks was conducted with TRACi and ReCiPe methods. Greenhouse gas (GHG) emission, eutrophication, fossil fuel depletion and metal depletion indicators were calculated and determinants of LCA of septic tanks were analysed. The system boundary was from cradle to grave. It was concluded that at the construction stage, GHG emission and fossil fuel depletion indicators are determined by the amount of concrete, steel, polyester resin, polyethylene, cast iron and PCV. At the use stage, GHG emission is determined by the amount and type of electricity used to treat sewage in a wastewater treatment plant (WWTP). Untreated wastewater, introduced into the environment (leaking tanks and users discharging sewage), is a determinant of infl uence on eutrophication. Life cycle inventory and environmental assessment of septic tanks with life cycle perspective are presented in the literature for the fi rst time. The results highlight the importance of including each stage in the environmental assessment of elements of the urban wastewater system.