OBJECTIVES: Data regarding willingness to pay (WTP) for one quality-adjusted life year (QALY) may need to be updated given rapidly changing modern lifestyles and dynamic shifts of population's values related to healthcare and economic factors as influenced by the COVID-19 pandemic. STUDY DESIGN: A cross-sectional study using online-based questionnaire surveys. METHODS: We conducted an online survey in March 2024 of 2,000 Japanese adults aged 20-69 years to evaluate their individual WTP for one QALY gained. We constructed a case scenario in which participants were asked to answer a series of yes/no questions to evaluate their willingness to pay for a new treatment to prolong a patient's life with a certain health status for one year. The scenario was stratified by the treatment cost per case, the annual number of patients, and the health status of patients. A probit model was implemented to estimate the WTP for one QALY gained and included the total cost, the total QALYs gained, recruitment method, participant's age, sex, household income, and educational background as explanatory variables. RESULTS: WTP per one QALY gained was estimated to be 16.98 [95%CI 14.43-19.91] million Japanese yen. A positive QALY gain (p <
0.001), male sex (p <
0.001), and higher household income (p <
0.001) were positively correlated with having a higher WTP. A higher total cost (p <
0.001), increased age (p = 0.002) and living alone (p <
0.001) were negatively correlated with WTP. CONCLUSION: Our study showed that the updated WTP threshold for a QALY gained was much larger than previously reported values. This suggests that WTP data should be reviewed and updated regularly.