The purpose of this study is to compare the seismic behaviors of interior post-tensioned (PT) and reinforced concrete (RC) flat plate slab-column connections designed to resist only gravity loads. In general, flat plate systems have been used to support gravity loads, which should be constructed with lateral system such as shear walls or moment frames. Flat plate systems should retain the ability to undergo the lateral drift associated with the lateral system without loss of gravity load carrying capacity. Although these systems are common, relatively little experimental study has been conducted to assess actual behavior under lateral loads. Therefore, this study was undertaken to assess the seismic performance of two PT and one RC slab-column interior connection under high gravity loads. This study observed that PT connections had a better seismic performance than corresponding RC connections in terms strength, deformability, energy absorption.