The tubular flames of lean methane/air mixtures in a rotating-flow field have been analyzed for their concentrations of stable species and temperature distributions, and their structures have been investigated. The results show that the tubular flame consists of an inner hot gas core of burned gas and an outer region of the unburned mixture, and that the flame structure is essentially the ssme as that of one-dimensional, flat, premixed flame. As the extinction limit is approached, the flame diameter decreases and the concentrations of carbon monoxide and hydrogen behind the flame zone increase. Hence, the extinction of the tubular flame of lean methane/air mixtures is csused by incomplete combustion with stretch as it is with other stretched flames. As the density inside the flame is lower than that outside, the flame front is rendered smooth and cylindrical by the rotational motion of the flow.