This paper presents the R1224yd(Z) flow boiling heat transfer and pressure drop measurements inside a mini microfin tube with internal diameter at the fin tip of 4.2 mm. The microfin tube was brazed inside a copper plate and electrically heated from the bottom. Sixteen T-type thermocouples are located in the copper plate to monitor the wall temperature. The experimental measurements were carried out at constant mean saturation temperature of 30°C, by varying the refrigerant mass velocity between 100 kg m-2 s-1 and 200 kg m-2 s-1, the vapor quality from 0.3 to 0.95, at three different heat fluxes: 15, 30, 60 kW m-2. The experimental results are presented in terms of two-phase heat transfer coefficient, onset dryout vapor quality, and frictional pressure drop. This new HFO fluid shows promising heat transfer capabilities, which makes it a possible viable substitute of the high-GWP, low-pressure refrigerants.