The purpose of this study was to investigate the changes of meteorological conditions, tympanic temperature and water intake during climbing mountain in the summer season. Seven men were volunteered to climb the Mt. Rokko (931m) that located in Hyogo prefecture. Tympanic temperature (Tty), water intake (WI), pulse rate (PR), rating of perceived exertion (RPE), atmospheric temperature (TA), relative humidity (RH), globe temperature (GT) and wet bulb globe temperature (WBGT) were measured at 5 different altitudes of mountain ascending(+) and descending(-) (P1: 30m, P2: 477m, P3: 621m, P4: 931m, and P5 at -400m). In shrub zone, the GT and the WBGT were elevated in the ridgeway (P2) compared with P1 and in the mountaintop (P4) compared with P3. In all subjects, Tty at P2 (37.3 ± 0.5 °C) increased significantly compared with those at P1, P3, P4 and P5 (p<0.05). WI between P1 to P2 and P2 to P3 increased significantly compared with those between P4 to P5. PR and RPE at each point within (P2～P5) were significantly higher than those at P1. This data suggests that meteorological conditions fluctuated with respect to the mountain geographical environment in the summer season. It was remarkable result that all subjects, Tty increased with an increase of WI and exercise intensity in shrub zone. In conclusion, this study could be attributed to better understanding of the human defensive mechanisms against heat stroke during mountain climbing in the summer season.