A variety of aromatic, aliphatic and conjugated aldehydes were transformed to the corresponding carboxylic acids with 70% t-BuOOH solution (water) in the presence of catalytic amounts of Bi2O3. This method possesses a wide range of capabilities, does not involve cumbersome work-up, exhibits chemoselectivity and proceeds under mild conditions. The resulting products are obtained in good yields within reasonable time. The overall method is green. © 2010 Elsevier Ltd. All rights reserved.