This study empirically analyzes whether the asset quality of the main bank is related to the firms" financial comparability. Most Korean companies engage in long-term relationship lending with the main banks. Through this relationship, banks can monitor the opportunistic behavior of managers. However, if the asset quality of the main bank deteriorates, the bank"s incentive to monitor can decrease. Thus we expect that the main banks" asset quality will be related to the firms" financial comparability. The results of empirical analysis as follows. First, we find a negative relation between the asset quality of the main bank and the firms" financial comparability. Second, this relation between the asset quality of the main bank and the comparability is stronger in firms with a lower level of corporate governance. Finally, we conduct additional tests for endogeneity and find that the results are consistent with our main hypothesis. This study has contributions by expanding the research on the determinants of comparability. In addition, our result that bank asset quality is related to firms" financial comparability has implications in that bank asset quality not only threatens the stability of the bank itself but also affects lending firms" decisions.