Ti-Ni shape memory alloys with and without Y were aluminized at 650℃ using pack-cementation method. The influence of various amounts of Y addition on the microstructure and isothermal oxidation behaviors of aluminide coatings in air at 700℃ was investigated. The aluminide coatings exhibited double layer structure even the aluminization progress is mainly controlled by inward diffusion of Al. Addition of Y promotes the growth of outer TiAl₃ layer, but retards the growth of inner NiAl₃ layer when Y is below 1at. %. Isothermal oxidation result indicated that the addition of 0.5 at. %Y significantly reduced scale growth rate. In contrast, 1at. %Y and 5at. % Y addition significantly increased the oxidation rate, especially the latter. The effect of Y on the coating formation and the coating oxidation behavior was discussed in details.