Abstract: An increasing attention has been paid to the use of duckweed in treating eutrophicated water as a tool of bio-remediation of domestic wastewater. Phosphorus uptake kinetics was studied, of different species of duckweeds, i.e. Lemna aequinoctialis, Spirodela oligorrhiza, and Spirodela polyrrhiza, which are common in the Yangtze River Delta area. Results show that the phosphorus uptake kinetics of the duckweeds could be expressed with the Michaelis-Menten equation; and the relation between phosphorus uptake rate (V) of the duckweeds and inorganic phosphorus (Pi) concentration (S), was well fitted with a double-reciprocal curve with α ＝0.01; the K_m value for Pi uptake of Lemna aequinoctialis was lower than that of Spirodela oligorrhiza and Spirodela polyrrhiza, making it a better candidate for treating wastewater low in Pi concentration. The maximum phosphorus uptake rate of Spirodela polyrrhiza was higher than that of the other two species, which allows Spirodela polyrrhiza better performance in purifying wastewater higher in Pi concentration.