A rod-shaped manganese oxide nanoparticles (MnO2) were successfully synthesized by a simple hydrothermal method. The phase composition, morphology, elemental composition, surface groups, and photocatalytic properties of nano-MnO2 were characterized using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and UV–Vis absorption spectrophotometry. The optimum reaction conditions are determined to be the reaction temperature of 120°C, and the reaction time of 12 h. Nano-MnO2 exhibited a uniform rod-shaped structure with a length in the range of 2–3 μm and the diameter of 50–60 nm. Furthermore, the prepared nano-MnO2 photocatalyst displayed the highest photocatalytic activity, with a methyl violet (MV) degradation ratio up to 89.5%, and the optimum nano-MnO2 dosage is 0.4 mg/mL. Besides, the nano-MnO2 sample possesses a stable and efficient photocatalytic performance after five recycling runs, demonstrating that the excellent recyclability and stability of sample under UV–Vis light irradiation. In summary, this result indicated that nano-MnO2 photocatalyst exhibited great promise as a means of effectively treating organic pollutants.