Project aims to simulate Mean Monthly Maximum Temperature (Tasmax) in summer of Northern, Thailand (2020-2030) using INMCM4.0 Model. Observation data of historical period were gathered from 14 Meteorological Department of Thailand, used to compare to Simulation data of same period to verify the model. Quantile Mapping (QM) was the best statistical downscaling method to predict future Tasmax with the lowest of %MPAE and MAE at 5.29% and ?1.85 oC. Tasmax values were presented in form of map by kriging method then trend changes were calculated by Mann-Kendall trend test and Sen?s slope. The results illustrated that the highest Tasmax was found around left-bottom of the region then fading in the next area to the top. Tasmax was gradually rising from February to May with the most range in hot (35.0 - 39.9?C) and very hot range (>40?C). Moreover, trend analysis indicated that the trend of February, March, April, and summer period were fluctuated and obviously increased at +0.111, +0.130, +0.121, and +0.063?C per year while it was at -0.007?C per year for May with the lowest and highest Tasmax values at 28.8 and 41.5?C. This can confirm that the region would have global warming issues in the future.