Since the establishment of 13.7m telescope in Taeduk Radio Astronomy Observatory (TRAO), Radio Astronomy is one of the active research fields in KASI and of Korea Astronomical Society. Its research activity has been enforced and deepened with installing and operating the Korean VLBI Network (KVN) in KASI since 2008. Currently KVN is in correlated operation with VLBI Exploration of Radio Astronomy (VERA) in National Observatory of Japan (NAOJ) and researchers in Korea-Japan VLBI Correlator Center work for the joint operations for this KVN-VERA program. Radio Technology Development Group (RTDG) in KASI has focused on the new millimeter wave receiver system with input optics that simultaneous observations in frour bands of 22, 43, 86, and 129 GHz to facilitate calibrating tropospheric phase fluctuations for millimeter-wave VLBI observations. RTDG also focusing on the development of prototype 230 GHz band SIS mixer for THz applications and other technology for the radio observation instruments.