This study reports the chemical composition of coconut water during its maturation. Composition was measured at 5, 6, 7, 8, 9, 10, 11 and 12 months maturation. Concentrations of sodium and glucose, and the osmolality values showed great variation throughout maturation. The concentration of sodium remained constant between the 5th and 7th months (mean 2.9 mEq/l), but increased after the 8th month (mean 12.5 mEq/l). The concentration of glucose remained constant between the 5th and 8th months (mean 3392.4 mg%), but abruptly decreased after the 9th month (mean 820 mg%). Osmolality followed the variation of the glucose concentration averaging 377.3 mOsm/l up to the 8th month, then decreasing to 310.3 mOsm/l after the 9th month. This study showed great variability in coconut water composition during maturation of the fruit. In no instance did the coconut water contain sodium and glucose concentrations of potential value as an oral rehydration solution.