In this study, the flow boiling heat transfer and pressure drop characteristics of R1234ze(E) and R32 in a horizontal multi-port tube with rectangular mini-channels of 1.13 mm in mean hydraulic diameter are investigated experimentally. The heat transfer and pressure drop characteristics are measured for the boiling flow in the mass velocity range of 100 to 400 kg/(m<sup>2 </sup>s) and heat flux range of 5 to 20 kW/m<sup>2</sup>. The pressure drop characteristics are also measured for adiabatic two-phase flow. The effects of mass velocity, vapor quality and heat flux on the boiling heat transfer characteristics are clarified. The measured frictional pressure drop and boiling heat transfer characteristics of R1234ze(E) and R32 are compared with previous correlations.