The whitening mechanism of hydrogenated silicon nitride (SiNx:H) film deposited on indium tin oxide (ITO) film was investigated by means of optical emission spectroscopy (OES), scanning electron microscopy (SEM) and X-ray photoelectron spectrosscopy (XPS) analysis. The degree of whitening of the SiNx:H film on ITO depends on the deposition conditions of SiNx:H, i.e., the SiH4 flow rate and the substrate temperature. Reactive species such as SiHn, decomposed from SiH4 gas, preferentially caused the reduction of ITO. This was followed by formation of In metal and a Si-rich porous layer containing SiO2. An abnormal growth of SiNx:H films caused by these successive reactions led to the whitening.