Global warming is becoming a major issue to the environmental perspective of view and one of the several causes is the release of refrigerants to the atmosphere. This research investigates refrigerant R-1234ze that is considered to substitute R-134a. A microfin and smooth tube with 9.5mm outer diameter was used in a twophase flow horizontal convective boiling to study the pressure drop and the enhancement of heat transfer coefficients. The brazed microfin inside a stainless steel tube was heated electrically with current. Thermocouples were inserted in the wall to measure the temperature distribution. The measurements were carried out at saturation temperature of 20°C by varying the refrigerant mass velocity between 50 kg/m2s and 200 kg/m2s, the vapor quality from 0.1 to 0.9, at different heat fluxes. Results from the two refrigerants and tubes were analyzed and compared basing on the values of the two-phase heat transfer coefficient and pressure drop.