CdS thin films were deposited by ILGAR ( ion laygas reaction) method.The effect of annealing temperature under N2 atmosphere on the structural, chemical, topographical development and optical and electrical properties of CdS thin films was investigated by XRD, SEM, XPS, UV- VIS and two-probe technique.It is found that the cubic-phase of as-deposited CdS film transforms to hexagonal phase with a perfected orientation along (002) plane at 300 ℃ .The band gap decreases with increasing annealing temperature until 300 ℃ , which is consisteat with the grain growth.The fall of dark and light resistivitiy is obvious with increasing annealing temperature, corresponding to the continuous grain growth and deviation of stoichiometry at higher temperature.The smooth and uniform surface of as- depositedfilms becomes rougher through thermal treatment, which is related to grain growth and sublimation of CdS at a higher annealing temperature.