On 4 October 1957, the USSR launched Sputnik-I, the first-ever artificial satellite, to outer space, which in turn triggered the space era. Shortly after the launching, COPOUS was set up by the UN General Assembly in 1959. Consequently, five principles were adopted on outer space during 1963 to 1966 involving Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space. The Committee also concluded five sets of space-related UN treaties until 1984 including the Outer Space Treaty (OST) which entered into force in 1967. Although OST is conceived to be most important among the aforementioned UN treaties, it has some vulnerability merely prescribing the placement of nuclear weapons and other weapons of mass destruction (WMD) into orbits around the Earth, while its passage, use and test are omitted in the statement as well as the deployment, passage, use and test of conventional weapons. As for the factors threatening space security, we can list space debris, loopholes of the OST, militarization/weaponization of outer space, development of space technology and anti-satellite weapons, dual use purpose of satellites for the civilian and the military etc. To minimize danger occurring from those threatening factors, reduce a gap from different space policies among nations, and ensure the space security, we need to promote transparency and confidence building measures, as sure substantiality of space activities, establish code of conduct and space traffic management, and have in-depth review on ‘The Draft Treaty on Prevention of the Placement of Weapons in Outer Space and of the Threat or Use of Force Against Outer space Objects'.