Novel Luffa cylindrica (LC) adsorbent modified with polyethyleneimine (PEI) was prepared by "grafting from" approach (LC-EPI-PEI) and "grafting-to" approach (LC-PGMA-PEI) and employed for the adsorption of U(VI) from seawater. The critical factors affecting U(VI) adsorption from aqueous solution were exploited, such as pH, initial concentration and contact time. The results showed that the adsorption of U(VI) on LC-EPI-PEI and LC-PGMA-PEI was strongly dependent on pH. The adsorption isotherm was satisfactorily simulated by the Langmuir model and the maximum monolayer adsorption capacities of U(VI) was 208.3 mg/g on LC-EPI-PEI and 438.5 mg/g on LC-PGMA-PEI. The accordance of kinetic data with the pseudo-second order model suggested that the adsorption reaction was controlled chemical process. In addition, LC-PGMA-PEI exhibited excellent reusability even after ten recycles. Moreover, LC-PGMA-PEI displayed excellent adsorption properties at low concentration of U(VI) (1.1g/L) in aqueous solution as well as in simulated seawater. (C) 2018 Published by Elsevier Inc.