Cubic Co9S8 fracture structure nanoshells and cubic Co3S4 nanocrystallines were prepared by ultrasonic spray pyrolysis process using cobalt chloride (CoCl2?6H2O) and thiourea (CH4N2S) as the starting materials. The as-prepared Co9S8 nanoshells and Co3S4 nanocrystallines were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) with energy-disperse X-ray spectroscopy (EDX) attachment and Fourier-transform infrared (FTIR) spectrometer respectively. It was found that the phase transition could be controlled by adjusting the reaction temperature, while morphologies of final products could be influenced by the molar ratio and reaction time of precursor. Meanwhile, possible mechanism for the formation of hollow and solid crystalline structures of the product was proposed.