A series of Ti2ZrHf0.5VNbx (x =0,0.25,0.5,0.75 and 1.0) refractory high-entropy alloys were prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties.All the alloys displayed a simple BCC structure.The microstructures of the alloys changed from the initial single-phase columnar structure (x =0) to dendrite microstructure (x ＞ 0).At room temperature,all the alloys exhibited high ductility (with the compressive strains of more than 50％).With the increase in Nb content,the yield strength slightly decreased from 1160 to 980 MPa and the hardness dropped from 338 to 310 HV.Moreover,the alloys exhibited low density from 6.47 to 6.84 g/cm3 and high specific yield strength (SYS) from 143 to 179 kPa m3/kg.The comprehensive performance of ductility and SYS was superior to most of the reported high-entropy alloys.The yield strength of the alloys increased from 405 to 859 MPa and from 85 to 195 MPa with the addition of Nb element at 873 K and 1073 K,respectively.