We present a facile and simple solid-state thermolysis approach for the formation of manganese oxide nanoparticles embedded in an amorphous carbon. This was accomplished through a single-step direct thermolysis of cetyltrimethylammonium permanganate. The as-synhtesized products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman microscope, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The product consists mainly of Mn3O4 and of MnOOH coated with carbon. The carbon coating was observed when reaction was carried out at 400°C and the average particle size is 9 nm. The shape of the products can be controlled by varying parameters such as reaction temperature. As the temperature increases from 500 to 700°C, larger spherical particles were observed without any carbon coating. The magnetic properties of as-synthesized products were evaluated using superconducting quantum interference devices (SQUID). The field-dependent magnetic measurements showed that nanoparticles embedded in carbon exhibited a high coercivity value of 10.5 kOe at 2 K. The saturation magnetization values at 2 K are 42 and 46 emu/g for the reaction temperatures of 500 and 600°C, respectively.