Istria County is one of the 21 administrative-territorial units in the Republic of Croatia. In the last few years, it has established itself as the leading Croatian county in the category of realized tourist arrivals, realized tourist nights and the number of accommodation capacities. One of the main reasons why tourists visit it is the favorable climate. Due to the fact that the climate will change in the future, ie that in the future there will be an increase in temperature and a decrease in precipitation, the County of Istria could lose some tourists. This reduction in the number of tourists can directly negatively affect the economy, tourism sector and development of this county. In order to determine the impact of climate change and how it will affect the tourism sector, the process of assessing the vulnerability of the selected sector to climate change is used. The process of assessing the vulnerability of the tourism sector of the Istrian County is the basic purpose of this research. When assessing vulnerability, 3 groups of indicators were used in the research, and they refer to the concepts of exposure,+ sensitivity and ability to adapt. One of the goals of this research was to identify the negative and positive consequences of climate change, and to identify key climate elements that will contribute to greater or lesser vulnerability. Also, the aim of this research was to create a tourist climate index that was not made for the reason that it was not possible to obtain data for mean daily air temperatures and mean daily relative humidity. The performed vulnerability assessment procedure of the tourist sector of the Istrian County determined that the highest vulnerability is in the tourist region of Poreč, and the lowest in the microregion of Labin / Rabac.