Water resources decreasing, changing time and precipitation type, low water quality, increasing drought and water demand, changes in the management of water resources as well as sea level rise and its complications are the significant impacts of climate change. Zayanderud basin is one of the most important basins of Iran which supplies the needed water for many towns and agricultural lands of central parts of Iran. Hence, the climate forecasting to use in basin major planning seems essential. In this research, climate change effects on monthly precipitation patterns of the basin were investigated using SIIRO3.5 and CGCMs under A and B1 scenarios using IDW and change factor methods for 2021-2050 as near and 2071-2100 as far periods. So, the average precipitation in each period was zoned using the kriging method. The results demonstrated that precipitation will decrease in the first period by 5 to 15%, but increase in the second period by both model . Precipitation will increase in the autumn up to 20-30% and decrease up to 20-25% in the winter and spring. Precipitation distribution of the basin has a minor variation in the future periods, so that it will decrease in the north east, central and the west parts of the basin but increase in the south and north parts. Basin thermal changes indicated that basin minimum and maximum temperatures will increase up to 2-6 ?C due to climate change. This will be higher in the 2071-2100 than 2021-2050 period. In CGCM3 model, the temperature increase in the summer and winter is higher by 2-3 ?C compared to CSIRO3.5 model. The basin climate map revealed that its climate will not have considerable changes regarding humidity in the future but the temperature will change from very cold climate to cold climate. Thermal changes of the basin can affect the water resources by changing the precipitation regimes, amounts and its type. Precipitation changes during different seasons can also have a significant impact on soil erosion and groundwater supplying. Thus, having the information, even with a low certainty, will lead us to have correct management of water resources and use alternative clean energies and fossil fuels to overcome the future problems. Keywords : Climate change, Downscalling, Change factor, Zayandeh-Rud