As the Final Document of the 12th Special Session of General Assembly pointed out, the nuclear arms race has continued unabated and the trial to prevent vertical proliferation of nuclear weapons has not been successful. On the other hand, the horizontal proliferation has been accomplished at least once by the Treaty on the Non-Proliferation of Nuclear Weapons, and in consequence, the r6gime of nuclear- and non-nuclear weapon states was formed. In such circumstances, it is an urgent and important problem to strengthen the security guarantees of non-nuclear weapon states. The regional approach proves as favorable for the enhancement of security through measures aiming at eliminating the nuclear risk, and the idea of Nuclear-Weapon-Free Zone has been revaluated increasingly. The Treaty of Tlatelolco is the most striking example of NWFZ and satisfies the next concepts: (1) the total absense of nuclear weapons in such a specified region (2) the establishment of the verification system (3) the obligation of nuclear states not to use or threaten to use nuclear weapons against non-nuclear states within the area. In the present paper, the conception, historical development and some legal problems concerning NWFZ would be reexamined in order to clarify that NWFZ is both a significant measure to contribute towards regional and international peace and security and an effective step for the general and complete disarmament.