We have investigated the nonlinear optical properties of indium tin oxide (ITO) thin film coated on soda-lime glass substrate using the z-scan technique. With 100 fs laser pulses, the nonlinear absorption coefficient and nonlinear refractive index are measured at different excitation wavelengths and at different incident intensities. The nonlinear optical absorption shows a competition between saturable absorption and reverse saturable absorption at the different excitation wavelengths and incident intensities. A transition from saturable to reverse saturable absorption was observed with increasing excitation wavelengths. The measured nonlinear refractive index was found to be dependent on wavelength with a maximum value of 5.34 x 10(-12) cm(2)/W at wavelength of 900 nm.