At the mechanical-biological municipal wastewater treatment plant, located in Poland in Mazovia Voivodeship, and its surroundings odour measurements using the field olfactometry method were conducted. During five measurement days 15, 21, 22, 20 and 22 receptor points were chosen. Receptor points were selected on the leeward side, at the edge and downwind at objects of technological line which were the most significant in terms of the potential for odour nuisance: the screen room, the longitudinal purged sand trap, primary settling tanks, the connecting chamber, chambers of phosphorus removal, the distribution chamber, chambers of activated sludge, secondary settling tanks, the tank of excess sludge, the digested sludge tank, the sludge processing building, where the sludge is dewatering, and in the surroundings of the sludge drying building. All measurements involved 2 trained assessors. For each measurement point (receptor) at least 2 replicates were made. Based on the conducted research, objects of the technological line with the highest value of the odourconcentrations and their ranges of impact were determined. The highest value of odour concentrations was equal to 43 ou/m3 and measured at the surface of the longitudinal purged sand trap and over the tank of excess sludge. Maximum odour concentrations in the vicinity of the distribution chamber, above chambers of phosphorus removal, above the connecting chamber, in the vicinity of chambers of activated sludge, at the edge of secondary settling tanks, in the vicinity of the screen room, next to open door to sludge processing building were 22, 6, 11, 4, 5, 16, 31 ou/m3 respectively. Range of impact defined as odour detection ofindividual objects did not exceed 50 m.