Fusarium sp. #ZZF51, marine-derived mangrove endophytic fungus, was chemically modified by poly(amic acid) to enhance its potential of uranium(VI) biosorption in aqueous solution. Compared with uranium(VI) removal of the pristine biomass, the maximum uranium(VI) adsorption capacity of the modified biomass increased 9.5-fold under the optimal condition of pH 5.0, S/L 0.4, and equilibrium time 180min. Kinetic study showed that the process follows the pseudo-second-order kinetic model, which indicates that chemical reaction controls the adsorption rate. The thermodynamic experimental data fit well with Langumir, Freundlich, and Temkin isotherms, and their R ( 2 ) values are 0.954, 0.963, and 0.986, respectively. FTIR spectroscopic analysis of the native, modified, and uranium-loaded biomass demonstrated the involvement of carboxyl, amide, and hydroxyl groups on the surface of fungus Fusarium sp. #ZZF51 cell wall in the adsorption of uranium(VI).