Zn1-xCoxAl2O4 (x=0, 0.20, 0.40 and 0.60) nanocrystals were successfully prepared via hydrothermal method using CTAB as surface active agent. The crystal structure, morphology, chemical composition, valence state and optical properties of the sample were investigated. The experimental results show that the samples are single phase spinel structure with good crystallization. According to the XRD data, the value of the crystal cell parameters, lattice spacing dhkl and grain size D were calculated, which show the decrease trend with the increase of doping concentration of Co ions. The XPS result clearly shows that the Co ions mainly occupied the tetrahedral site and a small amount of Co ions occupied octahedral center position. With the increasing of Co ions concentration, the ultraviolet absorption intensity is gradually increased.