A case study was undertaken to assess the long-term effects of irrigation with municipal waste water on heavy metals contamination of soil and leaf of black locust (Robinia pseudoacacia L.) trees. For this purpose, a field study was conducted at two sites irrigated by waste water and well water in the suburban areas of Tehran, Iran. Samples of irrigation water, soil and tree leaf were collected and were analyzed for Mn, Fe, Cr and Cd concentrations. Results indicated that municipal waste water had higher significantly (p<0.01) amount of Mn, Fe and Cr compared to well water. These heavy metals in waste water were upon the internationally recommended (WHO) maximum permissible limits set for land use. Heavy metals accumulation of soil was significantly greater in waste water-irrigated site and in depth of 0-15 cm. The mean of heavy metals concentration in soil was below the standard for all heavy metals. Fe and Mn concentrations in leaf of trees irrigated with waste water were significantly greater than those in well water but without risk. Cr and Cd were not detected in leaves and also Cd in water and soil samples. It was concluded that the use of waste water in irrigation might enriched soils with heavy metals to concentrations that may pose potential environmental and health risks in the long-term. Hence regulations about the utilization of waste water in irrigation should consider for control heavy metals content that may be added to soil, in order to minimize the risk of negative effects to ecosystem health.