The light emission produced by thiourea in oxidation process by permanganate in acidic solution in the presence of Ru(phen) 2+ 3 is used to determine 1.0×10 -8 |1.0×10 -5 mol/L thiourea. The limit of detection is 9.8×10 -9 mol/L and the relative standard deviation is 1.1% for a 1.0×10 -5 mol/L thiourea solution ( n =10). The method was applied satisfactorily to the determination of thiourea. The light emission produced by thiourea in oxidation process by permanganate in acidic solution in the presence of Ru (phen) 2+ 3 is used to determine 1.0 × 10 -8 | 1.0 × 10 -5 mol / L thiourea. The limit of The detection was 9.8 × 10 -9 mol / L and the relative standard deviation was 1.1% for a 1.0 × 10 -5 mol / L thiourea solution (n = 10). The method was applied satisfactorily to the determination of thiourea.