<p>In this paper, we report a new combined method of chemical coprecipitation-ionic liquid electrodeposition for the determination of trace uranium in seawater. The procedure involves coprecipitation of trace uranium on Fe(OH)₃ upon addition of ferric chloride and electrodeposition of uranium in EMIMBF₄ to determine by inductively coupled plasma optical emission spectrometry(ICP-OES). The solution, which ferric chloride was added to 1&#xa0;L of seawater sample and adjusted the pH to 4, was placed at 80&#xa0;°C for 30&#xa0;min to coprecipitate uranium with iron hydroxide. The precipitate was then dissolved in nitric acid and electrodeposited in EMIMBF₄ to determine uranium by ICP-OES. The coefficient of diffusion (D) of electrodeposition of U (VI) on platinum electrode in EMIMBF₄ was evaluated, which was 3.31 × 10⁻⁹&#xa0;cm²/s. The electrochemistry experiments indicated that the reduction of U (VI) at platinum electrode in EMIMBF₄ was a quasi-reversible single step two-electron transfer. The percent of chemical coprecipitation recovery of U (VI) was 98.9% and recovery in electrodeposition was 99.5%. Using combine of two methods can determined trace uranium in seawater.</p>