The primary purpose of this study is to identify the key dimensions of service quality in container terminals and to develop measurement instruments for them, and to examine whether the terminal service quality dimensions of container ports differentially affect customer satisfaction, loyalty, and word-of-mouth intention depending on "port location" and "customer size." The empirical results confirmed that the measurement instruments used in this study are classified into "internal quality," "external environmental quality," and "interaction quality." Reliability tests demonstrated internal consistency among the items constituting the factors included in the research model. The results of testing the moderating effects of "port location" and "customer size" revealed the following: First, for both Incheon Port and Busan Port, differentiation strategies through "interaction quality" were empirically demonstrated to be of primary importance. Conversely, urgent supplementary measures for "external environmental quality," including port cargo volume, hinterland complexes, and FTZ scale, were also found to be necessary. Incheon Port, in particular, was found to urgently need improvements to its currently insufficient terminal facilities. Second, Incheon Port was found to significantly lag behind Busan Port across all terminal service quality dimensions and customer satisfaction. Notably, "external environmental quality" did not have a significant effect on customer satisfaction, and "internal quality" was also evaluated as highly inadequate, indicating the need for urgent countermeasures. The significance of this study lies in its empirical analysis of the causal relationships between container terminal service quality, customer satisfaction, and loyalty—relationships that had not received sufficient attention in prior research. In the conclusion section, the academic significance and strategic implications for the logistics industry are discussed, and future research directions are proposed, including the identification of specific and particular service quality levels at each port terminal and additional verification of the external validity of the study's findings.