The use of waste water for irrigation is on the rise, particularly in peri-urban areas of developing countries. Effects of municipal waste water application on soil and eldar pine (Pinus eldarica Medw.) trees were studied. Two areas irrigated by municipal waste water and well water (for at least 15 years) were selected south of Tehran, Iran. Data was collected using the technique of systematic random sampling with 4 replicates in either or both fields. Observations included the measurement of tree diameter at breast height (d.b.h.), total height, crown length, average crown diameter, basal area and standing volume, needle mineral composition and changes in soil properties. Application of municipal waste water produced better growth in P. eldarica as compared with well water. Concentrations of N, P, K, Ca, Mg, Na, Cu, Fe, Mn, Zn as well as the values of pH, EC, SOC, CaCO₃ were greater in needles of trees irrigated with municipal waste water than of those with well water. All measured parameters of soil showed their greatest values in the upper layer of soil (0-0.15 m). Irrigation using municipal waste water did not result in toxicity of elements of needles and soil. This study confirms that municipal waste water could be utilized as an important source of water and nutrients in growing P. eldarica to increase biomass production.