Extracting uranium from seawater through an effective and economical adsorbent is a challenging task which is limited by (1) the extremely low concentration (similar to 3.3 ppb), (2) the presence of other metals ions with similar or even higher concentrations than U(VI), (3) the chemical and structural stability in seawater, and (4) implementation and environmental pollution problems. Therefore, it is desirable to develop adsorbents with superior adsorption capacity, excellent selective adsorption, robust chemical/mechanical stability and efficiency for treatment of large amounts of seawater. Herein, an acrylic acid (AA)/polyethyleneimine (PEI) modified Luffa cylindrical (LC) (LC-PAA-PEI) adsorbent, comprising the unique characteristics of PAA (3-D network hydrogel, large numbers of active sites and hydrophilicity), PEI (high adsorbability and selectivity for U(VI)) and LC substrate (3-D network fiber, high mechanical strength, stability, and eco-friendliness), was developed for the adsorption of U(VI) from seawater. The prepared adsorbent exhibited excellent adsorption properties with a maximum capacity of 444.4 mg/g and effective selectivity with a K-d value of 16944.4 mL/g for U(VI). Moreover, LC-PAA(5)-PEI1 displayed superior adsorption at low concentration (3-100 ppb) in simulated seawater.