A Ru/mordenite (Ru/M) catalyst with catalytically-active ruthenium species retained in the mordenite pores has been prepared by the ion-exchange of Na-mordenite with [Ru(NH 3 ) 6 ] 3 + , followed by a very mild thermal treatment. While extended X-ray absorption fine structure (EXAFS) analysis showed the presence of both Ru-N and Ru-Ru bonds, HRTEM photographs evidenced the absence of metal particles larger than the diameter of a mordenite pore. The remaining NH 3 ligand was also observed from the characteristic IR bands appearing at 1640 and 1356cm - 1 ; the IR spectrum of adsorbed CO indicated the presence of multicarbonyl-type surface species (such as Ru n + (CO) 3 ), consistent with the well-dispersed or coordinatively-unsaturated nature of ruthenium species. After the complete preparation procedure, a high degree of crystallinity was maintained for mordenite (XRD), and the decrease of S B E T from 362 to 313m 2 g - 1 ensured the existence of ruthenium species in the mordenite pores. It was demonstrated that, by using this catalyst, N-methylation of melamine with methanol was able to proceed in a moderately shape-selective manner (suppression of the formation of N,N',N''-tri-methylated melamine (3) as compared to that of N-methylated or N,N'-di-methylated melamine (1 or 2)), which is in harmony with the sizes of relevant molecules relative to the size of a mordenite pore.