This study reports the noninvasive, wide-field and rapid measurement of refractive index (RI) difference for diagnosis of cell's pathological state by utilizing light scattering with evanescent wave illumination. The RI of an abnormal cell is different from that of a normal one because of the change in the ratio of each intracellular component, thus RI measurement can be an effective approach for diagnosing cells. The present study focuses on the development of noninvasive RI difference measurement technique which can be applied to various biomedical analyses in the field of tissue engineering or drug discovery. When cells on a glass substrate are illuminated by the evanescent wave, scattered light whose intensity depends on the RI difference is generated at the interface between each cell and solution. In order to validate the effectiveness of this measurement method, the present technique was applied to the interface between PDMS and solution in the microchannel. The quantitative relationship between the RI difference and the scattered light intensity was obtained by adjusting the RI difference at the interface. It can be concluded that this measurement technique has possibilities to distinguish abnormal cells from normal ones by the scattered light intensity.