Osbeck"s grenadier anchovy(Coilia mystus),an important economic species, migrates with short distance between river and sea in the western Pacific Ocean．To understand the energy source during ovary development, the process of ovary development, feeding, and crude fat content in hepatopancreas, muscle and ovary of spawning groups of female Coilia mystus in the estuary of Yangtze River were analyzed. The results showed that：(1)Oogenesis in Coilia mystus was not synchronous. In the early period of reproduction(in late May),87% of the female individuals were in phase III and IV. The number of mature female individuals was gradually larger. By the end of the spawning period (in August), individuals of phase V accounted for 44.27%.(2)77% of phase III individuals, 90% of phase IV, and all phase V, VI had nothing food in the stomach and gut. In contrast, 93% of phase II individuals were at fullness of degree 1 and 2, indicating that Coilia mystus fed nothing in the spawning period and began to take food soon after spawning.(3)The muscle fat content of female individuals with phase III oogenesis was only 1.92% (wet weight, by chloroform-methanol extraction, although ovary gathered 62.43% of the total crude fat of the whole body. Thus, Coilia mystus allocated most energy to propagative organ, possibly this is why small fish is difficult to spawning migration for long distance.(4)In total, fat content in muscle and hepatopancreas decreased by 12.5% and 14.35% from phase III to VI respectively. Thereinto, fat content in muscle and hepatopancreas decreased by 7.29% and 3.65% from phase III to IV respectively, in comparison with decrease of 4.49% and 8.63% from phase IV to V respectively．This result suggests that the nutrition stored in the muscle mainly supplies for the migration and the early multiplication, while nutrition in hepatopancreas could boost energy supply for the subsequent spawning process.