ITO (Indium Tin Oxide) thin films is commonly used as transparently conductive electrodes for optical display devices, for example liquid crystal panel display, plasma panel display. Conventionally wet chemical etching has been used for patterning of ITO thin films. But this method has some problems such as many steps in process and it is not eco-friendly because waste fluid processing is required. Then we aim at establishment of laser ablation processing which is eco-friendly. As the 1st phase for that, we examined the effects of wavelengths on processing ITO thin films using diode-pumped Nd : YLF. There is a close relation to wavelengths and the transmissivity characteristic of ITO thin films, and processing form changes when wavelengths differ. And the debris of an edge portion became high when a slit was used in the fourth harmonic. Therefore cautions are required for adjustment of a slit.