Molybdovanadophosphoric acids (HPMoV) and their salts (NPMoV) partly substituted with an ammonium cation are efficient reoxidation systems for the Pd(OAc)2-catalyzed oxidation of alkenes and arenes with molecular oxygen. Acetoxylation of various cycloalkenes to 3-acetoxy-1-cycloalkenes was performed in good yields by the Pd(OAc)2/NPMoV/O2 system combined with hydroquinone. Oxidation of cyclohexene and styrene to the corresponding ketones by the same catalytic system in a mixed solvent of ethanol and water formed cyclohexanone and acetophenone, respectively, in fair to good yields. Monosubstituted alkenes such as ethyl acrylate and acrylonitrile underwent acetalization by this catalytic system to give the corresponding acetals in quantitative yields. Wacker-type oxidation of long-chain terminal alkenes by the present catalytic system was successfully achieved in the presence of a small amount of chloride ion. For example, oxidation of 1-octene formed 2-octanone (83%) as the major product, and the formation of undesired 3-octanone was less than 1%. The regioselectivity and yield of ketones were improved by dropwise addition of alkenes to the reaction system. The Pd(OAc)2/NPMoV/O2 system also acts as a good oxidation system for the carbomethoxylation of alkenes. Cyclopentene was carbomethoxylated under a mixture of CO (0.5 MPa) and air (0.5 MPa) to give dimethyl cis-1,2-and cis-1,3-cyclopentanedicarboxylates in good yields. Oxidative coupling reaction of benzene to biphenyl was performed by Pd(OAc)2 combined with HPMoV under dioxygen at 90°C. The best turn-over number of Pd(OAc)2 reached 109 and the yield of biphenyl was 14.3% based on the benzene used.