Abstract: Uranium can be detected at a sensitivity of 3.4×10~(-8) M by the polarographicwave produced by uranium with 7--bromo--8--hydroxy--quinoline-5--sulfonic acid(BHQS) at a pH of 4--5.The mechanism of the formation of this polarographicwave is found to be complexation--adsorption, as a result of the study of theeffect of Hg--column height, temperature, capillary charge, electrolysis at constantpotential etc. The complex of uranium with BHQS is shown to have a molratio of 1:1.