Abstract: To remove Th(Ⅳ) ions from wastewater, the adsorption behavior was investigated by mangrove endophytic fungus Fussarium sp.#ZZF51 that citric acid treated from South China Sea. The biosorption process was optimized at pH=4.5, equilibrium time 90 min, initial Th(Ⅳ) mass concentration 50 mg/L and adsorbent dose 0.6 g/L with 90.87% of removal efficiency and 75.47 mg/g of adsorption capacity, which is obviously greater than that (11.35 mg/g) of the untreated fungus Fussarium sp.#ZZF51 for Th(Ⅳ) biosorption under the condition of optimization. The experimental data were analyzed by using isotherm and kinetic models. Kinetic data follow the pseudo-second-order model and equilibrium data agree very well with the Langmuir model. In addition, FTIR analysis indicates that hydroxyl, amino, and carbonyl groups act as the important roles in the adsorption process.