In this paper a nationwide power quality monitoring system, which computes and collects PQ parameters and the required waveforms at a power quality monitoring center for both the purposes of early warning and later analysis of power quality of the whole transmission system, is presented. The system consists of three basic units: PQ monitors connected to various transformer substations all over the country; a national PQ monitoring center which communicates with all PQ monitors regularly, receives PQ data and archives them; and finally a client software, which lets individuals connect to the national PQ center and run searches on the PQ archive. The monitors compute PQ parameters based on the IEC Standard-61000-4-30. The client software will be available to the Electricity Transmission System Corporation of Turkey, TEIAS, distribution companies, large industrial plants which are directly supplied from the transmission system, research institutes and the universities. This is a three-year project of the Scientific and Technological Research Council of Turkey, TUBITAK, which started in March 2006 and the already-developed prototype system is presented in this paper.