Co doped Zn_1-xCo_xS nanorods with different concentration ratio (x=0, 0.01, 0.03, 0.05 and 0.07) were successfully synthesized by hydrothermal method using ethylenediamine as a modifier. The crystal microstructure, morphology and optical properties of the samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrometry (XEDS), Ultraviolet–visible Diffuse Reflectance spectroscopy (UV–vis DRS), photoluminescence spectra (PL) and Fourier transform Infrared spectroscopy (FTIR). The experiment results show that all samples synthesized by this method possess wurtzite structure with good crystallization, which indicates that all Co₂₊ successfully substituted for the lattice site of Zn₂₊ and generate single-phase Zn_1-xCo_xS. The morphology is one-dimensional rod-like shape with good dispersion. The the grain size increases, the cell volume decreases and the lattice constant occurs shrink with the increase of Co content. UV–vis spectra reveals the band gap of doped Zn_1-xCo_xS nanorods occurs red shift compare to that of the pure ZnS. PL spectra shows that the samples have obvious violet (402nm), blue (470nm, yellow (600nm) and infrared (826nm) emission peaks, the luminescence intensity decreases with the increase of the Co doping concentration.The FTIR spectrum shows that the absorption peak position does not change with the increase of the Co doping concentration.