R1234ze(E) has been created as an environmentally friendly substitution of R134a. An experimental investigation on adiabatic two-phase frictional pressure drop inside a 1.88 mm horizontal minichannel with R1234ze(E) and R134a was conducted. The saturation pressure and mass flux ranged within 0.6–0.9 MPa and 450–900 kg/(m2 s). Based on the 299 measured data points, the influences of various factors, including saturation pressure, mass flux, and the like, are examined detailedly. Larger mass flux brings about larger frictional pressure drop, and vapor quality performs the same function, but saturation pressure works inversely. The frictional pressure drops between R1234ze(E) and R134a present no significant differences. The experimental data are compared against 23 predictive models, among which the one from Xu and Fang (2013, “A New Correlation of Two-Phase Frictional Pressure Drop for Condensing Flow in Pipes,” Nucl. Eng. Des., 263, pp. 87–96) gives the best accuracy. In addition, a database including 3150 experimental adiabatic two-phase frictional pressure drop data points is derived from the current study and 29 published literature. Based on the database, the 23 models are assessed, and the most effective one is from Müller-Steinhagen and Heck (1986, “A Simple Friction Pressure Drop Correlation for Two-Phase Flow in Pipes,” Chem. Eng. Process., 20(6), pp. 297–308). This work can provide guidance for choosing appropriate two-phase frictional pressure drop models under adiabatic conditions.