In the presence of hydrogen peroxide as an oxidizing agent, the heteropoly anions H6P2W18O62, H6P2Mo18O62, alpha-K3PW9Mo3O40, alpha-K7PW9Mo2O39, H4PMo11Mo40, H5PMo10V2O40 and H6PMo9V3O40 were studied as catalysts for the N-oxidation of picolinic acid, in various solvents such as toluene, benzene and carbon tetrachloride. The highly selective oxidation, gave good to excellent yields of the related N-oxide along with decarboxylation at 2-position of ring. Among the catalysts tested, alpha-K3PW9Mo3O40 catalyzed the selective N-oxidation into related N-oxide product most efficiently, The effect of some operative variables, such as the mole numbers of hydrogen peroxide, amount of the catalyst, and the reaction time was studied. The reaction conditions were optimized. (c) 2006 Elsevier B.V. All rights reserved.