The initial flow characteristics of the turbulent circular jet discharging into the sudden expansion pipes have been investigated by the hot wire anemometry. Evolutions of similarity, centerline behavior, jet boundary and typical turbulent quantities were looked into for the expansion ratios. The results show that the spreading rates of discharging jet seem not to be dependent of the expansion ratio and that the velocity profiles in the radial directions exhibit the similarity in the regions, 2-5d, 2-6d and 3-8d for the corresponding expansion rations of 2, 3 and 5, respectively. With the increase of expansion ratio the centerline velocity decays rather slowly. The anisotropic behaviors of the discharging jets into the sudden expansion pipe look stronger than those of the free jet.