Abstract: Recently, heavy blooms frequently occured in Dianchi Lake and Microcystis is the main algae involved in blooms. Microcystis produces a family of related cyclic hepatopeptides(microcystins,MC). These toxins are severely hepatotoxic. Most investigations about the toxicity of the microcystins are focused on animals and terrestrial plants. To our knowledge,only a few studies have been made on the possible accumulation of microcystins on aquatic plants. This Paper evaluated the accumulation of MC-RR in Vallisneria natans,which is commonly used as food for fish or crab in some aquaculture places,using ELISA to quantify the amount of the heptotoxin accumulated. The results indicated that the roots and leaves of V. natans seedlings can absorb MC-RR. the amount of toxin accumulated in the roots and leaves of the seedlings is time and dose dependent, and the roots absorbed more toxins than leaves given the same condition. The absorption peaked after 7d’s exposure to the toxin and maintained this value in leaves, while the toxin in roots still accumulating after 16d’s exposure. The maximum amount of toxin accumulated in the roots and leaves is 14.83±0.12μg/g. FW and 0.32±0.026μg/g. FW respectively when exposed to the 10mg/L toxin solutions,and the numbers reduced to 0.59±0.083pg/g. FW and 0.28±0.016pg/g. FW when the toxin is at the concentration of 0.0001 mg/L. In contrast,the BCF value of the root and shoot increased from 0.13±0.013 and 0.035±0.0048 to 5.85±0.83 and 2.85±0.16 respectively. The results indicate that Microcystin-RR can accumulate in Vallisneria natans plant and raise the possibility that Microcystins could be thereby transferred into aquatic food web.