Surface modifications were performed on the tin-doped indium oxide (ITO) substrates for optoelectronic devices,using the different treatment methods (ultrasonic degreasing,aquaregia treatment,base (NaOH solution) treatment and oxygen plasma treatment).The effects of surface modifications on the surface properties of ITO substrates were characterized by X-ray photoelectron spectroscopy (XPS),atomic force microscopy (AFM),ultraviolet-visible (UV-vis) spectrophotometer,standard goniometry and four-probe meter,respectively.The surface free energy as the sum of the polar and dispersion components was evaluated from the measured contact angles using the Owens-Wendt approach.