Refrigerants in the evaporator have an important role in absorbing heat in the refrigeration system. However, the halocarbon refrigerants usage could damage the layer of ozone and causing global warming. Natural refrigerant is being developed to overcome the negative effects of using halocarbon refrigerants. MC-134 is one of natural refrigerant, a hydrocarbon refrigerant, that the main substances components are propane and iso-butane. This research will discuss the heat transfer coefficient value of MC-134 and the characteristics that affecting its value. The refrigerant is circulated in a heated pipe with 0.5 mm in diameter and 0.5 m in length. The result of the experiment is the variation of heat transfer coefficient between 678.42 - 5366.19 Watt/m2.°C. The value is determined by the heat flux at 149.3 - 7441.9 Watt/m2, the mass flux at 39 - 878.5 kg/m2.s, and the quality of vapor at 0.004 - 0.065. This research also shows that increasing heat flux will increase the heat transfer coefficient value.