This paper presents results of an experimental investigation of turbulent gas flow in microtubes fabricated by wire cutting electrical discharge machining (EDM) in a stainless steel block. The micro-Tube was designed with a main flow tube and five pressure ports, which lead to the pressure transducers. The average diameters of the main tubes were 320 μm and 369 ?m. And the aspect ratio of length to the average diameter is about 190. The outlet of the tube faced to the atmosphere. The pressure distribution of turbulent gas flow in microtubes fall steeply and Mach numbers increase near the outlet with increasing the inlet pressure due to flow acceleration. Both Darcy friction factors and Fanning friction factors of turbulent flow were obtained under the assumption of isothermal flow and under the assumption of one dimensional adiabatic flow. The later data reduction was proposed in the companion paper . Friction factors obtained under assumption of isothermal flow is compared with one obtained under the assumption of one dimensional adiabatic flow. The result shows that the obtained Darcy and Fanning friction factors were evaluated as a function of Reynolds number on the Moody chart.