The role of parts suppliers in the automobile industry is becoming increasingly important. Accordingly, this paper conducted an empirical analysis targeting parts suppliers of Korea's three major automobile companies to identify successful key supply practices for parts suppliers in the parts supply relationships of the Korean automobile industry. The results of this study revealed that the key supply practices for improving the production performance of parts suppliers in the Korean automobile industry are mutual trust and a cooperative atmosphere between finished vehicle manufacturers and parts suppliers, as well as the implementation of just-in-time supply by parts suppliers, rather than the use of information and communication technology between the two parties. In other words, parts suppliers that effectively implement just-in-time supply based on mutual cooperation achieve better production performance than those that do not.