Abstract: Phenophase and fruit cracking of Yuhuangyou pomelos(Citrus grandis Osbeck cv.Yuhuanyou)grown in open field and a greenhousewere compared.The changes on the fresh weight,color parameters,sugars and organic acids of the fruits in their development stages were observed.The results showed that the fruits ripened 10 ds earlier in the greenhouse than in the open field.The fruit cracking rate decreased 21% in the greenhouse as compared to the open field.Little difference in fruit weight was found between them.The color measurements of L,a* and b*on the fruits during maturation indicated that the greenhouse cultivation facilitated the color formation,more so than in the open field.Sucrose was the main component in the largely constant 76% of the total sugar content,with glucose and fructose accounted for 25%,in the pomelos.The greenhouse cultivation also allowed the fruits to reach its maximum sugar content one and a half month earlier than those inthe field.The major organic acid in the Yuhuanyou pomelo flesh was citric acid.It remained at a relatively low level throughout the entire fruit development stage.And,the greenhouse exerted no significant effect on the acid content in the fruits.The results showed that the greenhouse cultivation benefited fruit coloring,sugar accumulation,early maturation,cracking prevention and over-all quality for Yuhuanyou pomelos.