This article reviews the concept of urban density, and the documents and ratified regulations on the subject during recent years in Tehran.Although different aspects of density has been analyzed since then, but it seems that with the ratification of the new comprehensive plan of Tehran, taking a new look to this concept seems necessary.In fact, without understanding the true dimension of urban density, planning and design problems would be inevitable.One of the main human accomplishments of the last century in urban development is the focus on urban life quality and civic laws. Domination of quantitative approach to development and the lack of clear urban development strategies and legislative issues have been the principle reasons of the straggle of Tehran that caused its isolation from global urban development indicatives.Non-expert intervention in the matter, such as the selling of the surplus of residential density and to over-build the residential parcels in Tehran, and other big cities of Iran, seeking the benefit of a minority of investors, has lead to the loss of quality of urban environment. Unsustainability in many issues such as social safety, health and well-being of citizens is another consequence of this shortage.Throughout this article, a brief overview on the meaning of density (and its relating concepts) comes first. Then, as a sample of contemporary measures in urban density planning, and in a comparative framework, the zoning ordinance of New York and the equivalent documents for Tehran will be introduced and brought into discussion. Finally, the question remains that whether the new comprehensive plan of Tehran has considered the concept of density in a way that it could improve and ameliorate the environmental and social quality of citizens’ lives.