A floating-leaved plant (Nymphoides indica) community in an irrigation pond was investigated with respect to absorption and release of nutrients (N, P) and sheltering of solar radiation. In summer, the plant community grew up absorbing nutrients from the bottom mud, and then, both the values of the biomass and nitrogen content took a peak in July, however, the value of the phosphorus content exhibited a characteristic variation with two peaks both in July and August. In addition, multiplication of phytoplankton was largely suppressed due to sheltering of solar radiation by the floating-leaves in the plant community. In fall, the plant community released nutrients into the water body due to withering, and then, the value of Chl. -a greatly increased in the plant community with a time lag of about a month.