Refractory complex concentrated alloys (RCCAs) have recently attracted much attention due to their superior properties. However, the lack of room temperature ductility and strain-hardening ability has become a major challenge to be addressed. In this work, a novel metastable Zr-rich RCCA of Zr45Ti15Nb30Ta10 (at.%) was designed and studied. The phase stability of the novel RCCA was investigated by annealing at 600, 800 and 1000 °C, and its influence on the mechanical properties was revealed by tensile testing. The as-cast samples show a dendritic body-center-cubic (BCC) microstructure with one crystalline lattice constant, which displayed a yield strength of 901 MPa and an elongation of 13.4%. When annealing at 600 and 800 °C, the Zr-rich BCC1 phase and Nb–Ta-rich BCC2 phase were identified to form. The samples annealed at 600 °C showed a yield strength of 913 MPa and an elongation of 10.4% but an enhanced strain hardening capacity with an average strain hardening exponent of ∼ 0.88. This is attributed to the precipitated second phase hindering the movement of dislocations. The present work sheds light on developing novel RCCAs with high strength, high ductility, and considerable strain-hardening ability.