This paper focuses on experimental and numerical analysis of convective heat transfer characteristics of pressure-driven gaseous flows through microtubes, which is frequently encountered in practical application of microfluidic devices accommodating gas flow, heat transfer and/or chemical reactions at microscale. The present work has been carried out with the objectives to: (i) verify the applicability of conventional theory for the prediction of internal forced convection heat transfer coefficient for tubes having an inner diameter lower than 1 mm and (ii) check the performance of some specific correlations proposed for the analysis of forced micro convection with gases in the last decades. Single commercial stainless steel microtubes are tested with inner diameters ranging from 1 mm down to 0.17 mm. The most common thermal boundary conditions, namely uniform heat flux (H boundary condition) and uniform wall temperature (T boundary condition), have been implemented by applying Joule heating on external surface of microtubes (H b.c.) and by submerging microtube in water with constant temperature regulated by means of a thermostatic bath (T b.c.). The test section has been designed with care in order to ensure experiment reliability and to improve the accuracy of measurement at microscale. Experimental data are supplemented by numerical simulation, which demonstrates the local temperature distribution inside microtubes under various thermal boundary conditions. The values of Nusselt number are experimentally determined and compared with both conventional theory and the prediction of the specific correlations developed for microchannels.