To extend the duration of KMnO₄in the groundwater in situ remediation, controlled release oxidant was prepared by dispersing the KMnO₄particles in the molten paraffin wax. Preparation conditions, including KMnO₄particles size, ultrasonic treatment time and the weight ratio of KMnO₄to wax (P/W) were optimized. The results showed that the average volume particle size of 13.20 μm and ultrasonic treatment of 10 min contribute to the most uniform dispersion of the KMnO₄particles in the molten paraffin wax. The scanning electron microscope (SEM) images showed that the increased amount of KMnO₄caused the crushed structure of paraffin wax, which resulted in the higher porosity of wax to contain more KMnO₄. The KMnO₄loading amount increased significantly along with the increase of the P/W. However, the loading amount almost reached saturation by 609.63 mg/g when the P/W increased to 2/1. The releasing characteristics of the samples in the distilled water and the KMnO₄residual amount at different radial distance in the sample were examined by the bench scale tests. The releasing of KMnO₄could be divided into four periods and stable release took place after 40 d. Controlled release KMnO₄oxidant with P/W at 1/35 was used to remove COD in the leachate and 82.9% removal efficiency was obtained after 120 d treatment.