This study presents that the effect of green roof usage on the temperature decreasing for Turkey's cities has been investigated with Gene Expression Programming (GEP). Training data for GEP model has been taken from summer climatic data of nine different cities around the world, which have different climate regions. Thus, wide range of climatic conditions have been considered in GEP modeling. GEP model has been used for predicting the temperature decreasing over a green roof in Turkey cities. GEP model has given sufficient result with 2.2894% RMSE and 94.01% R-2. When the effect of green roof usage in Turkey cities is compared to World cities, it is found that temperature decreasing value for Turkey's cities and World cities has shown same trend. The maximum temperature increasing is 2.91 degrees C in Kars at 08:00 am. and the maximum temperature decreasing is 29.61 degrees C in Izmir at 06:00 p.m. (C) 2017 Elsevier B.V. All rights reserved.