Several researches dealing with the single-phase forced convection heat transfer inside micro channels have been published in the past decades. The performance of liquid flow has been proved that agree with the conventional correlations very well (Yang and Lin ). However, owing to the low heat transfer coefficient of gaseous flow, it is more difficult to eliminate the effects of thermal shunt and heat loss than water flow while measuring its heat transfer performance. This study provides an experimental investigation on forced convective heat transfer performance of air and gaseous carbon dioxide flowing through two microtube with inner diameter of 920 μm. A non-contacted liquid crystal thermography (LCT) temperature measurement method that proposed by Lin and Yang  was used in this study to measure the surface temperature of microtube. The test results show that the conventional heat transfer correlations for laminar and turbulent flow can be well applied for predicting the fully developed heat transfer performance in microtubes while taking account of the compressibility effect of high pressure gaseous flow in micro tubes. There is no significant difference between CO2 and air in both heat transfer and friction.