Fulvic acids (FAs) were extracted by alkali extraction from different soil samples in China, then purified using resins and characterized by Fourier transform infrared spectroscopy. The complexing ability of FAs was investigated by measuring the stability constants of rare earth elements (REEs) (La3+, Ce3+, Sm3+, Gd3+, Y3+) with FAs by the ion exchange technique. The results indicated that maximum binding ability forY3+ (4.41～4.44) was higher than other REEs (La3+, Ce3+, Sm3+, Gd3+) (0.72～1.03). There were two types of binding sites in the functional groups of fulvic acids. The complexing reaction followed two steps. The stability constants (K1 and K2) of REEs with Fas were calculated from experimental data by division of Scatchard plots into two straight-line segments. Y3+ (logK1=5.72±log K2=4.83±0.01) also has higher stability constants than the other four REEs (log K1=4.37±0.16, log K2=3.62±0.28).