This paper presents the comparative analysis of HFC134a and its low GWP substitutes HFO1234yf, and HFO1234ze(E) in saturated vapour condensation inside a 4 mm ID horizontal smooth tube. The experimental tests were carried out at 30, 35, and 40°C of saturation temperatures, with refrigerant mass flux in the range 100 - 600 kg m-2s-1 at decreasing vapour quality. A transition point from gravity-dominated and forced convection condensation was found in the range of the equivalent Reynolds number 10,000  20,000. The experimental heat transfer coefficients in the forced convection condensation regime were very well predicted by the Akers et al. (1959) model, whereas the Friedel (1979) correlation was able to reproduce the frictional pressure drop data in the whole experimental range. HFO1234yf and HFO1234ze(E) exhibit heat transfer coefficients and frictional pressure drops similar to those of HFC134a and both the HFO refrigerants seem to be very promising as long-term low GWP substitutes for HFC134a.