In order to reveal the effects of dopant average valence on the photocatalytic performance, Ta and Rh co-doped Ti0.96Ta0.04-xRhxO2 (x = 0, 0.008, 0.016, 0.02, 0.024, 0.032, and 0.04) samples were crystallized at 450 degrees C and 800 degrees C, respectively; then the 800 degrees C crystallized x = 0.02 sample was subsequently reduced in the H-2/N-2 mixture gases at 600, 700, 800, and 900 degrees C. Under different processing conditions, Ta remains the valence of +5, while the valence of Rh varies. Rh exhibits Rh3+ and Rh4+ in the 450 degrees C crystallized samples and is completely oxidized to Rh4+ in the 800 degrees C crystallized samples. In the reduced samples, Rh exists in the forms of Rh, Rh3+ and Rh4+. The optimal photocatalyst is obtained as the ratio of Rh3+/Rh4+ is 2.11 or the average valence of doped Ta and Rh is closest to the +4 valence of substituted Ti.