The characteristics of air temperature or heat mode the air is an important segment of the overall climate and the natural resource factor in the economic development of any place or region. In order to properly determine those, needs is a continuous series of data for at least 25-35 years. As longer as series are, the obtained data are more realistic. Weather Station-observatory "Tvrdjava" in Nis (φ-430 20 ', λ-21054', h-201 m), is the only higher-order station in the Niš valley, so, for determining the thermal properties of air, used measurement data from this station, for the period 1950-2009. Based on this 60-year period, analyzed the mean monthly, extreme temperature and annual temperature, the certain temperature thresholds and dates of onset for characteristic temperatures, and analyzed the frequency of occurrence some typical days.