About half a century ago, following the introduction of urban sprawl up concept, various studies have been conducted to describe the mechanism and the formation of this phenomenon. Some of these studies aimed at finding the negative and positive impacts of such phenomenon on urban area with emphasis on how such concept may be looked open from environmental, economical and social perspectives.The main research objective, in this article, focuses on adverse impacts of urban sprawl on air pollution in a mega city such as Tehran. Therefore, attempts have been made to show a relationship between urban sprawl up and the increase in air pollutants concentration. Three methods have been investigated to validate such a concept methodologically. Tehran has been chosen as a case study to further demonstrate validity of such a correlation between urban sprawl up and rise in air pollution scientifically. The results confirmed a function relating air pollution increase to urban sprawl up.