|This study has been conducted to investigate the molting behavior and the effects of rearing tempera-ture and day length on molting in the giant freshwater prawn, Macrobracbium rosenbergii reared in the lab-oratory. The results obtained were summarized as follow: 1. After pre-spawning molting, the protopodites of lst, Znd, 3rd, and 4th except 5th pleopod bore new breeding setae which conserve eggs in the brooding chamber and the basis of 3rd, 4th, and 5th pereiopods bore new breeding dresses which transport the ovulated eggs into the brooding chamber. 2. Adult females reared in 27.5-29.4”c molted lo-12 times per year at interval of 27-35 days, of which four or six moltings were common molting for growth and another four or five moltings were pre-spawning molting for spwaning and brooding. In winter season, pre-spawning molting did not happen to most of adult females in spite of the same temperature. 3. Duration of intermolt cycle was 31-38 days and 26-30 days at 25.3-26.5”c and 28.7-30.42 of rearing temperature, respectively.