Abstract: The uranium(Ⅵ) biosorption was studied in detail by using the biomass of mangrove endophytic fungus Fusarium sp.#ZZF51 from the South China Sea. The results show that the uranium(Ⅵ) biosorption process onto the tested fungus powders is optimized at pH=4.0, adsorption time 60 min, and uranium(Ⅵ) initial mass concentration 50 mg/L with 15.46 mg/g of adsorption capacity. The experimental data are analyzed by using the Langmuir model and the Freundlich model, and they provide better correlation with the experimental data for adsorption of uranium(Ⅵ). In addition, according to Fourier transform infrared spectra for Fusarium sp.#ZZF51 before and after loaded with uranium(Ⅵ), amino and hydroxyl groups range from 3.408 cm^-1 to 3.452 cm^-1, and the stretching vibrations of carbonyl band shifts from 1.649 cm^-1 to 1.631 cm^-1. By comparing with Fourier transform infrared spectra for the tested fungus before and after loaded with uranium(Ⅵ), hydroxyl and carbonyl groups have an important contribution to the adsorption process.