This study examines the effects of private health insurance (PHI) on the incidence of catastrophic health expenditures (CHE) for households with a patient with cancer. This study uses 1-year data from 2013 and households with cancer patients as the unit of research rather than individual household members. The sample thus includes 468 households with members with cancer who also used emergency, outpatient and hospitalisation services. Households with PHI had a lower incidence of CHE for all thresholds than those without did. At the 10% threshold, the incidence became significantly lower, by 0.59 and 0.60 times, respectively, if householders had higher education and income levels. Moreover, the incidence of CHE was higher by 8.71 times if the householders are female, and lower by 0.84 times if the householders did not have a spouse at the 20% threshold. From the analysis of households with cancer patients that hold PHI as the key variable, these households showed a lower incidence of CHE than the others did. PHI provides healthcare payments not secured through national health insurance (NHI) and protects households from health expenditures, thereby complementing NHI to a certain degree.