Abstract: Studies on the reproductive characteristics of Potamogeton maackianus A. Benn. were carried out under cultivation and in nature. P. maackianus, native to East Asia, is primarily wind pollinated and exhibits highly protogynous development: stigma receptivity prior to anther dehiscence. This is suitable for outcrossing, but stigmas are found to be still in receptive state when staminate stage begins, namely a "part overlapping" of male and female stages. The overall arrangment of stigmas, anthers and spatulate tepals is very beneficial for self pollination at the outset of anther dehiscence and suggests the possibility of autogamy. Low fruit set(20.16%)in nature may be attributed to short time of pollen viability(about 20h)and low rate of pollen germation(10%). Experimental evidences indicate that P. maackianus is self compatible, self pollination is presumably the derived condition and there is a tendency from outcrossing to selfing. Fruit set under isolated condition(13.6%)suggests that autogamy is an important component of the breeding system. Resource allocation to sexual reproduction is propotionally correlated with the degree of total biomass. P. maackianus shows different reproductive strategies in different habitats, and exists a sexual asexual evolutionary equilibrium.