Introduction: Since years ago the first coconut water has been used as tradicional medicine to cure various diseases. The content of glucose, electrolytes, vitamins, and proteins in the coconut water can serve as a replacement of body fluitds, as an energy source, and rehydration enhancer. Today there are a lot of isotonic drinks products marketed in the community. The drinks usually contain glucose, sodium, and potassium. Isotonic drinks are used in this study is almost the same composition with coconut "genjah salak" water.Objective: to know when the glucose levels increase and decrease after administration of coconut "genjah salak" water and the provision of isotonic drinks. The results of this study is expected to initiate the development of natural isotonic beverage as the replacement of body fluidsMethod: The research method is the human clinical trials testing using double-blind cross-over design of the experiment. The measured parameter is the measurement of glucose tolerance in the body per 15 minutes for 2 hours after the administration of coconut "genjah salak" water and the provision of isotonic drinks without doing physical activities during the measurement. Resullt: The glucose levels in the group given coconut "genjah salak" water and the group given isotonic drinks significantly increased, compared with the control group at the 15th , 30th and 45th minutes, but from 60th to 120th minutes there were no significant differences in the confidence level of α 0.05. Coconut "genjah salak" water group significantly increase at the 30th, 45th, and 60th minutes, compared with isotonic drinks at the confidence level of α 0.05. Conclusion: consuming coconut water can maintain and improve glucose levels required to replace body fluids. The body takes about 15-30 minutes to absorb the drinks in order to work effectively, so it is recommended to consume coconut water or isotonic drinks approximately 15-30 minutes before doing physical activities.