Manganese oxide (MnO) nanoparticle clusters embedded in a carbon matrix were deposited using one-step chemical vapor synthesis method for application in lithium ion battery. High resolution transmission electron microscope (HRTEM) and x-ray diffraction show the nanoparticles are polycrystalline with particle size ranging from 5 to 20 nm. EDAX, HRTEM, and X-ray photoelectron spectroscopy (XPS) revealed the presence of carbon in the sample matrix. Galvanostatic discharge-charge (GDC) experiments were performed on the clusters between 3.0 and 0.05 V vs. Li/Li⁺ at C/2, C/3 and C/5 rates. During the first discharge at C/3 rate, a semi-plateau is observed at ~1.0 V which is corroborated by cyclic voltammetry (CV) and delivered ~100 mAh/g. Then a plateau at 0.5 V yields ~500 mAh/g. An additional 200 mAh/g is obtained from the slopping region from 0.5 to 0.1 V, which the due to the pseudo-capacitance. The initial reversible capacity is ~800 mAh/g at C/3. The first charge curve has two plateaus at ~1.3 V and ~1.5 V corresponds to the oxidation of Mn⁰ to Mn⁺² and Mn⁺² to Mn^+3/+4, respectively. All subsequent curves show similar pattern. The capacity increases as the cycle number increases for both the discharge and charge. Ex-situ analyses of four identical samples cycled in the CV were carried in the at different cut-off voltages of 0.92 V and 0.28 V during reduction and 1.31 V and 2.13 V during oxidation. Interestingly, all four samples were still polycrystalline. XRD and HRTEM showed that the sample that was stopped 0.28 V (reduction) has the smallest particle size whereas the sample stopped at 2.13 V (oxidation) has the bigger grain size. The (111) reflection of the MnO nanoclusters was always present irrespective of the voltage cut-off. The (200) and (220) reflections of the (MnO) vanished during reduction and reemerged during oxidation and increased in intensity as the voltage increased. HRTEM revealed that carbon was present throughout the GDC and played a key role in the cyclibility of the MnO clusters by improving electronic conductivity.