An experimental study was performed on the behavior and extinction characteristics of the cylindrical diffusion flame affected by both factors of stretch and curvature. The cylindrical diffusion flame treated here has the convex curvature toward the air stream. The fuels used were propane and methane, and they were diluted with two kinds of inert gas, nitrogen and helium. The obtained results are described as follows. (1) The burner used in this study can form the cylindrical flame with good circularity. The minimum flame diameter is approximately 2.5mm. (2) The flame radius increases (decreases) with the increase in the fuel (air) flow velocity. (3) Flame luminosity has a maximum value when the air flow velocity is varied. On the other hand, the luminosity decreases monotonously with the increase in the fuel flow velocity. (4) Extinction stretch rate of counterflow propane 20%/nitrogen 80% vs. air flame is lower than that of counterflow methane 50%/nitrogen 50% vs. air flame. However, this extinction stretch rate relation is reversed in the case of cylindrical diffusion flame owing to the Lewis number effect caused by the flame curvature. (5) When the Lewis number of fuel flow is considerably larger than unity, the cylindrical diffusion flame can be formed even at the dilution rate with which the counterflow diffusion flame cannot be formed.