A study on the improvement of wear resistance of brasses by electroplating and diffusion treatment of tin was carried out. The optimum condition of the treatment obtained was as follows. Plating thickness of tin : 5 - 9 $mu extrm{m}$ Condition of diffusion treatment : atmosphere ; fused nitrate bath (KNO3 + NaNO3) temperature and time ; 1st step 320$^{circ}C$, 60min. and 450$^{circ}C$, 30min. During the diffusion treatment, internetallic compounds of Cu-Sn were formed and these compounds were identified as η, $varepsilon$ and $delta$ phase from the outer tin layer. It was considered that the improvement of wear resistance of brasses by the treatment is because of the formation of intemetallic compounds particalarly $varepsilon$phase which is very hard, between soft tin layer brass.