The pitching oscillation and the flow field around blunt-body reentry capsule at transonic speeds are studied by transonic wind tunnel experiment using two different model shapes. Dynamic instability such as pitching oscillation greatly influences the flight control and landing accuracy of a capsule, hence understanding the flight characteristics is a significant. In this study, we focus on the influence of flow separation and reattachment on the aft-body, and perform the experiments using a one-degree-of-freedom free-rotation test method. The effect of aft-body shape is investigated by comparing the resulting differences in pitching oscillation tendency and flow field. The results show that dynamic instability is strengthened in a shallower aft-body angle model. It is possible to see from examining the flow field visualization results that there are notable differences on the flow separation and reattachment and its hysteresis. It is speculated that these differences influenced the pitching oscillation in a shallower aft-body angle model.