In this study, the phase distribution of a horizontal branch T-junction acting as a phase separator for application in thermodynamic cycles was investigated experimentally to make a better understanding of the separation mechanism of refrigerant two-phase flow. All the internal diameters of the tubes for the T-junction were 8.0 mm. All experiments were conducted using refrigerant R134a. The investigated factors included the inlet mass flux, the quality and the mass flow ratio being varied in the range 300 to 500 kg·m⁻²·s⁻¹, 0.1 to 0.9 and 0.3 to 0.7, respectively. Effects of these factors on the outlet quality, the mass flow ratios of vapor and liquid phases and the pressure drops were analyzed. It was found that the vapor is more likely to turn the corner into the branch. As the mass flow ratio increases, the mass flow ratios of vapor and liquid phases increase. However, the increase of mass flow rate has no obvious influence on the phase distribution. For the pressure drop at the T-junction, as the quality and mass flow rate increase, the pressure differences increase. Compared with the inlet pressure, the branch pressure is always lower, while the direct pressure is generally higher.