Ethanol production by agricultural waste is now focusing area in bioenergy field to reduce the environmental pollution. The fruit wastes are highly biodegradable; therefore they can be preserved for a long time and may well be used for further processing. The watermelon is usually used throughout the summer which produced a huge amount of wastes every year. It is very important to manage this waste because of its easy degradation and causing pollution in environment. The study investigated the ability of yeasts to convert the watermelon hydrolyzate to ethanol by fermentation and optimization of hydrolysis condition. In optimization, variable factors were hydrolyzate concentration (X1), hydrolysis temperature (X2) and incubation period (X3) and the responses were ethanol contents, reducing sugars and yeast growth. Watermelon peels were hydrolyzed by different alkalis i.e. sodium hydroxide, potassium hydroxide and calcium hydroxide. In sodium hydroxide hydrolyzate, the observed optimum values of ethanol contents were 14.22±0.55 with standard yeast Saccharomyces cerevisiae K7 at 75mL hydrolyzate, 25ᵒC temperature and 15 incubation days. The model is significant with P-value of 0.0007 for ethanol contents. With yeast Mitchnikowia sp. Y31, the maximum ethanol content were 10.54±2.21. In potassium hydroxide, the maximum value of ethanol contents was 8.82±0.02 with standard yeast Saccharomyces cerevisiae K7. The significant ethanol yield 10.65±0.45 was observed by Metschkowia sp. Y31. The model was significant for ethanol contents. In calcium hydroxide, the maximum ethanol 7.58±0.26 was observed with yeast Mitchnikowia sp. Y31. With standard yeast, Saccharomyces cerevisiae K7 maximum ethanol 9.38±0.61was observed. The model was significant for ethanol contents with P-value 0.0117. 12