Mono-dispersed molybdenum disulfide solid spheres with the diameter of 0.5-2 mu m have been successfully synthesized by a solvothermal method with a homemade quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) as surfactant. The obtained solid spheres are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The influences of reaction conditions are discussed while a mechanism is proposed to explain the formation of the peculiar morphology.