This study has been conducted to evaluate the effect of varying concentrations of urea fertilizer on the growth, protein, fat and water content of five aquatic plants, in aquaculture system. These plants were cultured in glass basins outside the laboratory in tap water and they received doubling doses of urea fertilizer (1, 2, 4, 6, 8 and 16g) per 30 L medium at three days intervals. The media were changed before receiving the following inoculum and the excess yields were harvested. Potamogeton crispus, P. pectinatm and Ceratophyllum demersum eould withstand urea concentrations up to 533 mg/L, while Polygonum amphibium could survive at 133 mg/L, but Azotta filiculoides died at the same concentration. Crude protein increased, generally during the experiment, in all test plants except in P. crispus that showed wide fluctuations. Fat content decreased in all plants by the end of the experiments, but water content fluctuated slightly between increases and decreases during the experiment.