Nowadays, more and more attention has been paid to the new low GWP (global warming potential) refrigerant R1234ze(E), which is one of the ideal alternatives for R134a. In this work, the flow boiling heat transfer coefficients of R1234ze(E) and R134a were measured inside an 8 mm ID horizontal tube. The experimental results were obtained over the saturation temperature of 10℃ with heat fluxes ranging from 5.0 to 10.0 kW·m~(-2) and mass fluxes ranging from 300 to 500 kg·m~(-2)·s~(-1). The influences of mass flux, heat flux and quality on the heat transfer coefficients were discussed. The results showed that the local flow boiling heat transfer coefficients of R1234ze(E) and R134a increased with increasing mass flux and heat flux. The local heat transfer coefficient of R1234ze(E) was around 14.68% lower than that of R134a at the mass flux of 300 kg·m~(-2)·s~(-1), while the local heat transfer coefficient deviation between R1234ze(E) and R134a reduced to 7.35% when the mass flux reached 500 kg·m~(-2)·s~(-1). Additionally, the experimental data of local heat transfer coefficients were compared with four well-known correlations available in literatures. The results indicated that Kandlikar correlation provided the best prediction of the local heat transfer coefficients for both R1234ze(E) and R134a. Approximately 90% of the experimental points are in an error bandwidth of 25% of the prediction, and the average deviations are found to be 23.13% and 11.50% for R1234ze(E) and R134a, respectively.