This paper proposes one new attempt to formulate a mathematical approach to climate parameters in the context of their complex implications for tourist activities through the tourism climate comfort index (TCCI). This paper also aims to formulate an original and optimal mathematical correlation between readily obtainable climate parameters (mean monthly air temperature, monthly amplitude of air temperatures, monthly insolation, average monthly relative air humidity and the number of rainy days), which results in values of the TCCI. Simultaneously, this index will provide the values correspondent to the values of air temperatures (°C), which represents a comparative baseline understandable equally for tourists, tourism planners and managers. The example of Serbia as a mainland country in the south-east of Europe was used to apply the proposed methodology. The spatial-temporal variability of TCCI is formulated on basis of data for the period 1961-2000 while for testing model was used selected period 2001-2010 on the sample of 26 meteorological stations distributed all around Serbia. For this purpose a standard statistical techniques were applied and ArcGIS software was used for analyze of the variability of the TCCI in relation to the altitude, which is of particular importance for the development of tourism in the mountains. Checking variability of the index was carried out in relation to statistical data about number of tourists on the three most visited tourist destinations which are of importance for the development of urban, mountain and spa tourism, the leading forms of tourism activities on the territory of Serbia. The obtained results correspond with the fact of the pronounced seasonality of tourism market and thus may represent a good basis for future tourism planning and management.