Citrus trees(Citrus sinensis L. osbeck)and their supporting soils were sampled for investigation of Hg uptake by the perennial plant and its relationship to soil properties and humic-substance-bound Hg (HS-Hg) in the soil. Results showed that in acidic soil, the more acidic the soil was, the less Hg the citrus trees absorbed. Hg content in fruits was negatively correlated with the contents of organic matter or humic substances in the soils. HS-Hg, especially the FA-Hg fraction, was the major Hg source for citrus trees. Correlation coefficients between citrus root Hg and soil HS-Hg reached 0.700^*~0.759^**. Surface soil could provide more available HS-Hg than sub-surface soil.