Manganese doped iron oxide nanoparticles based on the chemical formula Mn_xFe_3-xO₄ (where × = 0.00, 0.50, and 1.00) have been prepared with different concentrations of manganese-oleate, and iron-oleate by thermal treatment method. To prevent nanoparticle from agglomeration and increase surface functioning, oleate was employed as a capping agent to create stable nanoparticles for magnetic particle imaging (MPI). Mn-doped magnetite nanoparticles (Mn_xFe_3-xO₄) were synthesized by the thermal decomposition method. Manganese-based iron oxides were morphologically assessed by x-ray diffraction (XRD), fourier transformed infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Manganese-based iron oxides were also magnetically examined with electron-spin resonance (ESR), physical properties measurement system (PPMS), and magnetic particle relaxometer (MPR). Additionally, phase composition and iron concentration of the manganese-based nanoparticles were determined with the Mossbauer spectra (MS) technique. The crystallite size of 11–18 nm was achieved with the XRD technique for Mn_xFe_3-xO₄. MnFe₂O₄ (x = 1.00) revealed high stability at higher temperatures according to TGA analysis and high saturation magnetization at room temperature as compared to other manganese concentrations. MPR demonstrated the shortest relaxation time of MnFe₂O₄ as compared to commercially MPI tracer agents such as Vivotrax (magnetic insight) and Perimag (micromod). The finding of this study emphasizes that manganese ferrites have the immense potential to become the optimum tracer agent for MPI applications.