Abstract: A simple, selective and highly sensitive procedure for spectropho-tometric determination of uranium has been developed. In pH 6.0-8.5, uranium reacts with chromazurol Sand amphoteric-nonionic mixed surfactant to form a blue complex, which has absorption maxima at 615 nm. The molar absorptivity at 615 nm is 1.1-1.2×10⁵. The composition of the complex is established as U: CAS = 1:1 by the methed of job and the equilibrium shift. Beer's law is obeyed for 0-50 μg/25 ml of uranium. The complex is very steady,that could allow the presence of masking agents in a great amounts. Thus, a great majority of metal ions do not disturb the determination of uranium.In this paper, the formation conditions of the complex was studied, it was also researched to enchance sensitization mechamism using mixed surfactant. In this work CyDTA-Tar mixed masking agent was adopted and a minute amount of uranium in ores containing high-thorium, high-rare earths and high-zirconium, respectively, has been determined without separation.