The electro-mechanical mercury relay is used as an auxiliary relay of power facility because it is superior to operating time and no-bounce. So the KEPCO had used the mercury relay for operating HVDC(High Voltage Direct Current) system. But it has many problems with facility operation by occurrence of mercury evaporation, held contact point and malfunction according to long term use, furthermore it is forbidden to produce for fear of environmental pollution in 2002. This paper presents the no-mercury relay development, comparison test and application.