In this study, it was aimed to evaluate the NO2 levels in four key cities of Turkey (Istanbul, Ankara, Izmir and Bursa) over a three-year period and to examine the effect of NO2 on mortality. The research is of descriptive-ecological type. In the research, air quality (NO2), population and death data were needed for each city to cover the dates 01.01.2017-31.12-2019. In the research, 20 μg/m3 was accepted as the annual NO2 limit value. Numbers, percentages, mean, standard deviation, minimum and maximum values were used in summarizing data. Calculations related to mortality attributed to NO2-induced air pollution were made using the AirQ+ software’s own methodology. In 2019, 33 stations in Istanbul, 4 stations in Ankara, 5 stations in Izmir and 5 stations in Bursa were measuring NO2. In 2019, the weighted NO2 mean was 40.61 μg/m3 in Istanbul, 32.94 μg/m3 in Ankara, 7.87 μg/m3 in Izmir and 31.68 μg/m3 in Bursa. The estimated percentage of deaths attributed to NO2 in 2019 was 7.95 in Istanbul, 5.07 in Ankara and 4.58 in Bursa. Calculations for 2018 in Ankara and 2017, 2018 and 2019 in Izmir were not made because the NO2 levels in these cities were less than 20 μg/m3 in these years. As a result of the research, it was determined that the NO2 levels were higher than the limit value in three of the four key cities in Turkey and the mortality rates attributed to NO2 were found to be higher compared to similar studies in the literature.