Carbon nanotube(CNT) based Gas sensors are at- tracting huge research interest as it gives high sensitivity, quick response, and stable sensors for industry, biomedicine, and more. The development of nanotechnology has opened a new gateway to build highly sensitive, cheap, portable sensors those who have low power consumption. The extremely high surface to volume ratio and the hollow structure of nanomaterials is perfect for the adsorption of gas molecules.Mainly, the advent of carbon nanotubes has boosted the inventions of gas sensors that exploit CNTs unique morphology, geometry, and properties. Upon exposure to some gases, the changes in carbon nanotubes properties can be determined by many methods. Therefore, carbon nanotube-based gas sensors and their mechanisms are widely studied. In this paper, a broad survey of current carbon nanotubes based gas sensing technology is presented. few experimental works done are reviewed. The types, fabrication, and the sensing mechanisms of the carbon nanotubes based gas sensors are discussed. The challenges of the research up to some extent are also addressed in this paper.