Abstract: This paper reports studies on the effect of rare earth elements (REE) on nitrogen assimilations in the sugarcane. After foliar application of REE to sugarcane plants in 5 different concentrations, change in the contents of nitrate nitrogen, ammonium nitrogen, total nitrogen, free amino acid, free amino acid composition, nitrate reductase (NR) activity were determined. The experimental results showed that, treating sugarcane leaves with REE at 100-600 ppm concentrations, could in varying degrees decrease the content of nitrate nitrogen and Increase the contents of ammonium nitrogen, total nitrogen, free acid and NR activity, this tendency being most apparent at the 300 ppm concentration. High concentrations, however, exhibited opposite effects. REE treatment In sugarcane decreased the content of nitrate nitrogen and increased that of ammonium nitrogen, being consistent with previous reports that NR activity increased after REE treatment. That is to say, NR activity was positively correlated with nitrate nitrogen. No change was found in the free amino acid composition at different concentrations of REE in the leaves of the sugarcane, but the free amino acid content varied rather much, notably with the 300 ppm treatment These results showed that nitrogen assimilation in the sugarcane could be promoted by certain concentrations of REE treatment,