The Massachusetts health care reform was expected to reduce the financial burden of medical care, but literature exploring this effect is limited. In this study, we use hospital financial information and a panel data difference-in-difference model to assess the impact of the Massachusetts health care reform on unpaid medical bills. We find that the reform reduced the financial burden for patients, reflected by a 26percent decrease in hospital bad debt. The effect was more pronounced among safety-net hospitals, indicating a larger benefit for the most vulnerable population.