The new ruthenium(II) complexes having pentadentate ligands. [RuCl(N4PY)]Cl and [Ru(N2PY2O) (Me2SO)] were prepared. 1 2 Catalytic oxidation of adamantane using MCPBA or 2,6-dichloropyridine N-oxide as cooxidant has been examined. Using N-oxide in the presence of a small amount of MCPBA or Ce(IV) ion (0.5-5 mol%, vs substrate) the ruthenium complexes exhibit considerable catalytic activity, and that with the ligand having carboxylate groups is found to he more active.