Zn_0.97TM_0.03O (TM = Co, Fe) thin films were deposited onto glass substrates by the sol–gel method and the effects of transition metals substitution on structural and optical properties of ZnO films were investigated. The X-ray diffraction patterns revealed that the films have wurtzite structure. Optical transmittance of the films was recorded in the range of 200 -800 nm wave length and the band gap of the films was determined. The absorption edge of the films showed a small shift depending on the substitution elements. The optical constants of the films were calculated by using pointwise unconstrained minimization algorithm.