Cupric oxide (CuO) thin films were prepared by chemical bath deposition (CBD) method on glass substrates using copper chloride solutions and then annealed at 300 °C in Argon atmosphere in different time intervals of 1 and 2 h. Samples were characterized by FESEM images, XRD and UV-Vis. spectra. We found that the as-grown nanostructured sample has a single-phase (CuO) monoclinic polycrystalline structure with preferred direction of (-111), but after annealing an addition Cu₂O phase is also appeared. Analysis of the absorbance data showed that with increasing the annealing time the optical band gap of the sample decreases.