This study tests the validity of the alternative hypotheses in the intra-industry trade (IIT) literature using information on Korea’s trade between 1991 and 1999. The study refines previous studies by breaking down IIT into horizontally and vertically differentiated products, controlling for country fixed-effects, and using more variables relevant to Korea’s industry data. The main results suggest that some conflicting results of previous empirical studies could be caused by the use of the aggregate approach itself. Most of all, variations of the level of IIT in Korea are better explained by vertical IIT. Furthermore, while the hypotheses derived from the theoretical models of horizontal IIT and vertical IIT are generally confirmed by the empirical analysis, the hypothesis of demand similarity was not supported. The results also favor the competitive market structure explanation for both types of IIT in Korea.