The purpose of this work is to study regional climate change and investigate the effects of urbanization on climates of two largest cities in Turkey: Istanbul and Ankara. Air temperature (mean, maximum and minimum) data of istanbul and Ankara are analyzed to study regional climate change and to understand the possible effects of urbanization on the climate of these regions owing to industrialization and large flux of migration from rural parts of the country. For the trend analysis, linear regression and the sequential version of the Mann-Kendall test is used. A significant upward trend is found in the urban temperatures of southern istanbul, which is the most highly populated and industrialized part of the city compared to its rural parts. Northern stations do not show any warming trend; instead, they have a cooling trend. Urbanization and industrialization in the southern part of istanbul has a negative effect on regional cooling. In spite of Ankara's urban geometry and air pollution problem, the urban station in Ankara does not show any warming trend. A significant urban heat island intensity (urban-rural) is not observed in Ankara.