Abstract: The bi-exponential decay of the luminescence of electronically excited uranyl ions in perchloric acid has been investigated with detailed study of the time resolved lu-minescence spectra and Raman spectra of uranium. While the U(Ⅵ) concentration is in the range of 0.01-0. 1 molL~(-1) and the pH is≤1.5, the luminescence decay is sin-gle exponential and the luminescence spectra are independent on the delay time and the U(Ⅵ) concentration with peaks at 488.0, 510.0, and 533.0 nm, which belong toaquo-uranyl ions. While the pH of the solution is increased to higher than 2.8, the luminescence undergoes bi-exponential decay and the luminescence spectra with 0.2 μs delay time change dramatically with increasing the pH and the U(VI) concentration, and are different from the spectra with 20 μs time delay, which consist of three peaks at 500.0, 518.0, and 538.0 nm. From the thermodynamic data of the hydrolysis of uranyl ions and the dependence of the Raman spectra of U(VI) on the pH and the uranium concentration the later spectra can be identified as the spectra of the dinuclear hydrolysis product of UO~(2+)_2 and (UO_2)_2(OH)~(2+)_2. All the measured time resolved spectra can be fitted to the linear combination of the spectra of aquo-uranyl ions and (UO_2)~(2+)_2(OH)~(2+)_2 satisfatorily. The conclusion that the bi-exponential decay is attributed to UO_2(H_2O)~(2+)_x and (UO_2)_2(OH)~(2+)_2 ions has been withdrawn.