We developed a new SCADA system for 500-kV substations. To apply existing LAN-based SCADA system for unmanned 275-kV or 77-kV substations, we had to develop three functions. Firstly, the new SCADA system enables that 500-kV substation is supervised and controlled from multiple operating sites. Secondly, the database of the new SCADA system can be downloaded the maintenance data from the SCADA system for 500-kV control center via an IP network. Finally, the new SCADA system has supervisory control capability for manned 500-kV substations. In this paper, we describe these functional over view of the new SCADA system. Currently, 500-kV substations are manned substations. And these substations are supervised and controlled by human operators on sites. Using the new SCADA system, 500-kV substations will be realized remote supervisory control from the 500-kV control center a few years later. Therefore, manned 500-kV substations will convert into unmanned substations.