Exercise is highly essential for a healthy life. The athletes drink water to restore the body fluid volume and salt ingredients during the exercise. It is postulated that the blood parameters of athletes would greatly be affected if they run more than 10 km in controlled dehydration (without taking liquid) in a hot environment. This study aims to investigate the acute hematological changes in Saudi male athletes engaged in sports activities in a hot climate without taking fluid. In this cross-sectional study, the participants were adult Saudi athletes (n=12) who ran for a 10 km distance during the daytime when the temperature was ≥35°C. Blood samples were collected before and after the race and analyzed by standard methods for hematocrit, plasma volume, hemoglobin, total white cells count, red cells count, and blood lactate was examined. The mean age of athletes was 22.83 years; their mean height was 173.8 cm, and the mean weight was 56.1 kg. The average body fluid loss during the race was 1.88 ± 0.70 L. The white blood cells, hematocrit, hemoglobin levels were increased significantly at the end of the running event (p < 0.05). However, values of red blood cells and insulin were decreased. Exercise, mainly the running race in hot weather conditions, has a significantly increasing impact on athletes' hematological and biochemical parameters. The findings have an important message for the sports trainers and coaches to prepare prospective professional athletes and improve their performance for national and international sports events.