Two-phase flow pattern and the frictional characteristics of refrigerants R-407C and R-125 inside a 3-mm-diameter tube are reported in this study. Tests were performed with a mass flux in the range of 300∼1000 kg/m2·s. It is.found that the development of flow pattern for R-125 is at a lower vapor velocity than that of R-407C, due to its larger vapor density. A modified flow-regime map applicable for a 3-mm-diameter tube is developed by modifying the abscissa axis of superficial vapor velocity in the conventional-flow map. This flow pattern map is capable of describing the present data set along with that of Yang and Shieh (2001). Test results of the frictional pressure gradient are compared with several empirical correlations. It is found that the Friedel correlation shows the best predictive ability, having a mean deviation of about 20%.