The article aims to assess the effectiveness of the non-proliferation regime established more than 40 years ago with the adoption of the Treaty on the Non-proliferation of Nuclear Weapons (NPT). Since that time the international community had achieved considerable success in the prevention of nuclear weapons’ proliferation. Nevertheless, while noting the results of the NPT and the verification system established under that instrument, one cannot remain silent about the shortcomings of the system and the non-compliance with some of its provisions. By its structure and provisions the NPT has divided States into two groups, distinguishing those possessing and those not possessing nuclear weapons. In effect, the rights and obligations of the Contracting Parties to the NPT are tailored to the group to which they belong, and the gravest violation of the NPT is that when States seek to change their status as defined in the NPT, notably by trying to munfacture or control of nuclear weapons. Under the NPT, research in, production and application of nuclear energy for peaceful purposes are inalienable rights, but their exercise should be in keeping with the basic obligation of nonnuclear-weapon States under the Treaty not to acquire in any form nuclear weapons and not to carry out unauthorized nuclear activities under the guise of their peaceful nuclear programs. While emphasizing the need to strengthen the non-proliferation regime, the article describes in nutshell the nuclear program of two States (the Islamic Republic of Iran and the Democratic People’s Republic of Korea) which gave cause for serious international concern.