Rare earth Gd-doped ZnO thin films were prepared by a simple sol-gel spin coating method in order to search for a new functional diluted magnetic semiconductor for potential application in spintronics. The thin films were deposited onto glass substrates with zinc acetate dehydrate, monoethanolamine and 2-methoxyethanol as a starting material, stabilizer and solvent, respectively. The dopant percentage was increased up to 8%. Optical investigation showed that the crystallinity of the thin films was changing due to the increase of the Gd concentrations and optical band gap energy (Eg) value was estimated to be around 3.12 ~ 3.28 eV using Tauc's model. The crystallite size determined from XRD spectra and the results was found that the value is in the range of 14.42 ~ 21.98 nm.