Abstract: In the paper, a new method for determination of trace silicon in the oxide of uranium with ethylrhodamine B, silicate, molybdate acid and PVA developer system is described. In the solution of 0.3 mol/L HCl, silicate and molybdate form a heteropoly acid. In the presence of PVA as stabilizater, ethylrhodamine B and the heteropolyanion form a stable ternary associated compound when the acidity of solution is about 0.5 mol/L. At λ588 nm, the molar absorption coefficient(ε) is 1.7×10 5 L·mol -1 ·cm -1, the minimum determination limit for silicon is 2 μg/L.