Background: The purpose of this study is to evaluate the effect of health insurance coverage expansion for cancer patients on equity in health care utilization and catastrophic expenditure. Methods: To analyze the causal relationship between the policy to expand benefit coverage and the change in health care utilization and out-of-pocket payments of cancer patients, this study employed a difference-in-differences (DID) method. In the DID model, the change in health care utilization, such as health care expenditure, visit days and length of stay, of cancer patients was compared with that of liver disease patients, using Korea Health Panel Data in 2009 and 2010. Results: The policy of reducing cost sharing from 10% to 5% for cancer patients did not have significant effects on equity in health care utilization. The results of this study were different from those of the previous study that showed that the reduction of cost sharing from 20% to 10% significantly improved the equity in health care utilization of cancer patients. In addition, the result of catastrophic expenditures analysis showed the policy did not change the probability of catastrophic expenditures. Conclusion: The results of this study imply that payment for non-covered services account for high out-of-pocket payments, and the reduction in cost sharing for covered services alone may have a limited effect on total financial burden on patients.