AbstractDecentralization can alter the incentive structure of local governments and one outcome of this is debt accumulation. Based on the “Province‐Managing‐County” pilot policy, a fiscal decentralization reform devolving fiscal power from the prefecture‐level city to the county level, we assess the impact of fiscal decentralization on local government debt using a difference‐in‐differences model with a unique county‐level dataset from 2011 to 2019. According to the study findings, the “Province‐Managing‐County” reform resulted in an average increase of 5.758 percent in the local government debt ratio across the pilot counties. Mechanism analyses suggest that this may have arisen from changes in the incentive structure, including external pressures from government assessments and internal developmental needs for promotion, leading to a rise in expenditure pressures on local governments. The role of supervision in mitigating the impact of fiscal decentralization on debt growth was also demonstrated, indicating that an appropriate supervision mechanism must be in place in conjunction with a decentralization policy.