This paper presents experimental results on heat transfer characteristics of laminar gas flow in a microtube with constant wall temperature whose wall temperature is lower than the inlet temperature (cooled case). The experiment was performed for nitrogen gas flow through microtubes with 163 and 243m in diameter and 50mm in length. The gas was heated in an upstream section of the microtube to T-in approximate to 315K, 335K, and 355K. The wall temperature was maintained at 305K by circulating water around the microtube. The stagnation pressure was chosen in such a way that the exit Mach number ranges from 0.1 to 0.7. The outlet pressure was fixed at the atmospheric condition. The total temperature at the outlet, the inlet stagnation temperature, the mass flow rate, and the inlet temperature were measured. The numerical computations based on the Arbitrary-Lagrangian-Eulerian (ALE) method were also performed for the same conditions of the experiment for validation of numerical results. The two results are in excellent agreement. The total and bulk temperatures obtained by the present study are also compared with the temperature of the incompressible flow.