In this study, unsteady flow analyses have been performed for three dimensional wing/tail configurations using a computational method based on a transonic small disturbance(TSD) equation. The good agreements are obtained between the present TSD code and the XTRAN3S of NASA Langley Research Center. The steady flow results of TSD code have been also compared with those of Euler equation in transonic and supersonic regimes. In the case of wing/tail configurations, aerodynamic interference effects of lifting surfaces have been investigated for several Mach numbers. Steday pressure and spanwise life distributions are computed and compared to illustrate the interfernce effects. Unsteady aerodynamic analysis results due to wing and tail pitching motion are also presented.