The present work investigated the effect of reduction-oxidation(R-O) pretreatment on the CO oxidation activity of Co3O4/Al2O3 catalyst. After the reduction-oxidation treatment, the crystalline size of Co3O4 supported on the Al2O3 decreased and it exposed more Co3+, resulting in the improvement of CO oxidation activity. Compared with the as-prepared conventional Co3O4/Al2O3 catalyst, the Co3O4/Al2O3-R-O catalyst is easy to be reduced at lower temperature. The surface reconstruction occurred during the reduction-oxidation pretreatment accounting for the improvement of the catalytic activity. This study reveals the importance of R-O pretreatment as a strategy for the improvement of supported metal oxide catalyst with advanced catalytic performance.