Cobalt ferrite nanoparticles are synthesized using biological agents as fuel by both conventional and microwave heating methods. We focused on the green synthesis of cobalt ferrite, which is eco friendly, inexpensive, and easy to produce by large-scale synthesis. Synthesis methods were carried out under the same conditions. The role of the plant extract and advantages of microwave techniques are discussed. Plant extract-mediated nanoparticles were characterized by various techniques to analyze the size, shape, crystallinity, optical, magnetic, and antimicrobial properties. The X-ray diffraction pattern revealed single-phase crystalline structures with an average size of 45–55 nm. The functional groups present in the samples were confirmed by Fourier transform infrared spectroscopy. From SEM and DLS studies, it is confirmed that the spherical nanoparticles range in the size of 300–500 nm for CHM and 5–50 nm for MHM. Energy-dispersive X-ray spectroscopy analysis confirmed the presence of cobalt, iron, and oxygen. The energy band gap of the samples was measured by UV–Visible diffuse reflection spectroscopy. In photoluminescence analysis, the band emission was observed in the visible region. Samples prepared by microwave heating showed better magnetic behavior than those prepared by conventional heating based on vibrating sample magnetometer analysis. The plant extract makes the synthesis of cobalt ferrite nanoparticles a potentially low-cost and ecofriendly remediation method. The synthesized nanoparticles also exhibited excellent antimicrobial activity against bacteria and fungus strains. © 2017 Elsevier B.V.