In the present study, we report the green synthesis of novel magnetically separable MgFe2O4 nanoparticles using Cajanus cajan (L.) Millsp leafs via combustion method. The MgFe2O4 were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and UV-diffuse reflectance (UV-DRS) spectroscopy. The crystalline structure of MgFe2O4 was confirmed via XRD studies and TEM showed that the MgFe2O4 NPs were distorted spherical particles with particle size ranging between 5 and 15 nm. UV-DRS study showed the optical band gap of MgFe2O4 NPs to be 1.8 eV. Microwave-assisted (MW) degradation of PCM-dolo drug using MgFe2O4 as catalyst was performed at different operating parameters such as time (30 min), drug concentration (PCM-dolo 50 mg/L), initial concentration of MgFe2O4 (0–110 mg/L), and microwave power (100–600 W) to obtained the degraded fragments of the drug. Experimental data was used to compute the degradation efficiency of PCM-dolo on MgFe2O4. The enhanced catalytic performance could be ascribed to the production of MW-induced active species, such as holes (h+), superoxide radicals (⋅O2−) and hydroxyl radicals (⋅OH) in the degradation process. A possible degradation mechanism and pathway was proposed.