Radiotherapy remains a mainstream treatment for patients with unresectable and locally advanced esophageal squamous cell carcinoma (ESCC). However, intrinsic radioresistance of ESCC tumors has largely compromised the efficacy of radiotherapy. The following study investigates the potential radiosensitizing effect of alpinumisoflavone (AIF) and explores its underlying mechanisms in ESCC. Briefly, our results showed that AIF could significantly increase radiosensitivity of ESCC cells both in vitro and in vivo, by increasing the effect of AIF on irradiation-induced DNA damage, apoptosis and cell cycle arrest. Mechanically, AIF aggravated irradiation-induced ROS generation in ESCC cells, which occurred via suppressing the expression of nuclear transcription factor Nrf2 and Nrf2-driven antioxidant molecule NQO-1 and HO-1. Collectively, we concluded that AIF functions as a potent radiosensitizer in human ESCC