Directly extracting uranium from alkaline solution and seawater through an effective and economical method is still a challenging task. In this work, we for the first time propose a method of anionic exchange, based on a cationic MOF (metal-organic framework) adsorbent, namely Co-SLUG-35, to directly extract U(VI) from alkaline solution and seawater (South China Sea). The U(VI) adsorption experiments indicates that the EDS2- anions in Co-SLUG-35 can be completely replaced by U(VI) ions in an anionic manner, leading to an adsorption capability of 118 mg/g from alkaline U(VI) solution and excellent extraction efficiency of 1.05 mg/g from 1 L actual seawater in the concentration of 5.35 ppb. Most importantly, unlike other MOFs where degassing is primarily needed, however the use of present MOF need not any pretreatment. Moreover, ultrahigh selectivity towards U(VI) ions even over Cro(4)(2-) and CI- ions is also observed in Co-SLUG-35, suggesting its superior potential in extraction of uranium from seawater. (C) 2017 Elsevier B.V. All rights reserved.