Catalytic activity is the main obstacle limiting the application of peroxymonosulfate (PMS) activation on transition metal oxide catalysts in organic pollutant removal. Herein, ultrasonic treatment was applied to α-MnO₂ to fabricate a new u-α-MnO₂ catalyst for PMS activation. Dimethyl phthalate (DMP, 10 mg/L) was almost completely degraded within 90 min, and the pseudofirst-order rate constant for DMP degradation in the u-α-MnO₂/PMS system was ∼7 times that in the initial α-MnO₂/PMS system. The ultrasonic treatment altered the crystalline and pore structures of α-MnO₂ and produced defects on the u-α-MnO₂ catalyst. According to the XPS, TG, and EPR results, higher contents of trivalent Mn and oxygen vacancies (OVs) were produced on the catalyst surfaces. The OVs induced the decomposition of PMS to produce ¹O₂, which was identified as the main reactive oxygen species (ROS) responsible for DMP degradation. The u-α-MnO₂ catalyst presented great reusability, especially by ultrasonic regeneration of OVs toward the used catalyst. This study provides new insights into regulating OVs generation and strengthening catalyst activity in the PMS activation process for its application in water purification.