The different effect of oxygen vacancy variation on photo-assisted degradation effect and structural phase transition of oxygen defective Ba(Fe,Co)O3-x in dye degradation were investigated via comparative studies. The samples of perovskite BaFeO3-x and BaCoO3-x were synthesized at 700 degrees C by citrate sol-gel method. Samples synthesized above 700 degrees C show oxygen deficiency. With oxygen vacancy increasing, the BaFeO3-x becomes instable, whereas BaCoO3-x improves the stability. The instability is due to CO2 adsorption activity of oxygen vacancies, and then this may make negative effects on their photo-assisted degradation effect. So finally, the oxygen vacancies take different effects on photo-assisted degradation effect of Ba(Fe,Co)O3-x. (C) 2011 Elsevier Ltd. All rights reserved.