We propose the method of measuring the refractive indices (RI) of transparent films using White Light Scanning Interferometry(WLSI). Fourier-transformed interferogram is represented as a DC-term and the sinusoidal term whose amplitude is the product of the sample reflectance and the energy term which is determined by the reference mirror and a light source. Once we get the interferogram data of the reference sample whose RI is known, we can obtain the energy term of the WLSI system. After obtaining the energy term of the WLSI system, we measure the interferogram data of the sample whose RI is unknown under the same experimental conditions. Combining these energy terms and the interferogram, we get the RI of the sample for each wavelength.