Urban areas are characterised by the impact of negative environmental factors, such as: stress connected with extreme bio-thermal conditions or the presence of high concentrations of air pollutants. This study aims to evaluate the relationship between the hours of O3 concentrations and the levels of physiological strain (PhS) in Legnica, during the period from December 2013 to November 2014. The hourly concentrations of O3, NO2 and meteorological elements used in the study were obtained from the State Environmental Monitoring station in Legnica (Lower Silesia). The evaluation of the bio-thermal conditions was carried out by means of the physiological strain indicator (PhS). The basic statistics were subject to analysis, the frequency of hourly pollution concentrations and the thermal strain were evaluated, as was the Pearson correlation coefficient and multiple regression between O3 and PhS. A detailed analysis was carried out for the summer months (June-August). The most adverse conditions in terms of pollution with tropospheric ozone and heat strain were noted in July. The strongest relations between O3 and PhS were observed in June. In winter months (December-February) no significant dependencies were noted between the tested variables. These tests will help to contribute to increasing the current knowledge on evaluating the thermal comfort of urbanised areas and the accompanying aero-sanitary conditions.