The cowpea weevil, Callosobruchus quadrimaculatus, has two distinctly different forms in the adult stage, fly and non-fly forms, which are induced by the effect of population in the larval stage. These two forms are very like to the "phase" dimorphism observed in the locust and army worm. In the present paper, different densities of comparisons were made between these two phases in their body weight and the chemical constituents of their body. The body weight of adult weevil decreases with the lapse of adult life, but this decreasing tendency is different between these two phases and sexes. (ref. Fig. 1, fly female _??_, fly male _??_, non-fly female _??_, non-fly male _??_). The water content of the body takes an almost constant value throughout the life, but takes a different value in each phase (ref. Fig. 2. similar sign as in Fig. 1). Crude fat content shows a definite difference between these two phases. That of the fly phase is higher in both sexes. A clear difference can be found in the acid value and iodine value of the crude fat, while there is no definite difference in saponification value. From these data, we can imagine that the fly phase has a kind of diapause in the initial stage of adult life.