The phosphorus compounds in the ovaries of various developmental stages fromthe adult Chinese farm fishes, Hypophthalmichthys molitrix, were analysed accordingto the methods of Schneider 1945 and Schmidt and Thannhauser 1945. At the sametime, the contents of water, protein and fat of the ovaries were also estimated withthe usual biochemical methods. In the ovaries of young developmental stages Ⅱ and Ⅲ, the acid solublephosphorus compound (A) and ribonucleic acid (RNA) are significantly higher thanthe other phosphorus compounds-the phospholipid (L), phosphoprotein (Pp) and deoxyribonucleic acid (DNA). The phosphorus content of the former two compoundsconstitutes more than 85% of the total phosphorus in the young oyaries. As thedevelopment advanced, the phosphorus contents of L and Pp increase promptly duringstage IVa to IVc, while those of the A and RNA decrease during the same stages.The increasing features of the total protein and fat are essentially the same as thoseof L and Pp. Although the contents of these phosphorus compounds manifest differently in aunit weight of various stages of ovaries, the total amount of all these constituentsin one ovary increase in considerable extent during the development here considered.The most prominent feature is the increasing scale of the amounts of L and Pp, whichincrease 980- and 1,333-times respectively within the course of ovarian developmentstudied. These changes seem to bear relation to the formation of yolk in the oocytesand the histological development of the ovary. As the variation in the contents of these phosphorus compounds is considered, itis obvious that the major increase of L and Pp occurs mainly in the stage IV of deve-lopment, which lasts from February to April for Hypophthalmichthys molitrix in ourdistrict. This means that such a vast increment of the ovarian materials may besynthesized in a short period of 2 to 3 months. Therefore, it is obvious that, inpractice, a sufficient food supply in the spring is indispensable for the ovariandevelopment of the brood fishes to be used in the artificial propagation. This mayoffer from the theoretical aspect a technical guidance for the acceleration of thesexual maturity of the brood fishes in the pisciculture. The changes in terms of the percentages of the different phosphorus compounds indifferent stages lead to the conclusion that the developmental process of the fishovary may consist of two phases of synthesis: (1) the early phase, ranging fromstage Ⅱ to stage Ⅳa, is characterized by the synthesis of protoplasm shown as an abun-dance of A and RNA; (2) the late phase including the stage Ⅳ as a whole, ismarked by the synthesis of yolk indicated by an immence increase of L and Pp. The biological significance of the formation of these phosphorus compounds inthe ovarian development of the fishes studied is to incorporate the energy-rich phos-phates into organic constituents in the oocyte as well as to synthesise a large amountof organic substances as reserve materials both for the embryonic development of theeggs after fertilization.