Abstract: Eight rice genotypes viz. KS-282, IR-6, DR-83, NR-1, NIAB-6, DR-82, Lateefy and JP-5 were tested under the environmental conditions of D.I.Khan at 171.6 meters above sea level. The mean minimum and maximum temperature during the experimental season ranged between 14 and 42°C. The effect of high temperature on the genotypes was observed as reduction in yield and yield components like plant height, number of tillers per hill (Tillering ability), days to 50 percent flowering, seedling vigour, 1000-grain weight and grain yield. A considerable amount of genetic variability was observed at each growth stage in the season. The environmental effect on commercial variety IR-6 and the newly evolved variety KS-282 in tillering ability and 1000-grain weight indicated non-significant and significant differences, respectively. It is therefore, concluded that while selecting for high temperature tolerance the material should be tested in the actual hot areas and screening should be made in the target environments.