Purpose: This study was done to investigate factors affecting perceived financial burden of medical expenditures. Method: The participants were 2,024 inpatients who were enrolled in a survey on the benefit coverage rate of the National Health Insurance in 2006. The collected data were analyzed using t-test, ANOVA-test, Mann-Whitney-test, Kruskal-Wallis-test, Chi-square test and logistic regression. Results: The crucial factors for perceived financial burden were age, job, equivalence scale, ratio of annual family income vs medical expenditure, and private health insurance. Perceived financial burden was higher for people who were older, who were unemployed, whose medical expenditures were high compared to annual family income, whose index of family equalization was low and for those who had no private health insurance. Conclusion: The results of the study indicate a demand for system reform that will enable management of no-pay hospital bills in the National Health Insurance to decrease the medical expense of people in the low-income bracket.