Body-centered-cubic　(BCC)　refractory　high-entropy　alloys　(RHEAs)　are　being　actively　pursued　due　to　their　potential　to　outperform　existing　superalloys　at　elevated　temperatures.　One　bottleneck　problem,　however,　is　that　these　RHEAs　lack　tensile　ductility　and,　hence,　processability　at　room　temperature.　The　strategy　previously　invoked　to　sustain　ductility　in　high-strength　HEAs　is　to　manage　dislocation　movements　via　incorporating　dispersed　obstacles;　this,　however,　may　also　have　embrittlement　ramifications.　Here,　a　new　strategy　is　demonstrated　to　achieve　ductile　BCC　HfNbTiV,　via　decomposing　the　BCC　arrangement　(β　phase)　into　a　β(BCC1)　+　β∗(BCC2)　arrangement　via　spinodal　decomposition,　producing　chemical　composition　modulations　and,　more　importantly,　elastic　strain　on　a　length　scale　of　a　few　tens　of　nanometers.　The　periodically　spaced　β∗,　with　large　lattice　distortion,　is　particularly　potent　in　heightening　the　ruggedness　of　the　terrain　for　the　passage　of　dislocations.　This　makes　the　motion　of　dislocations　sluggish,　causing　a　traffic　jam　and　cross-slip,　facilitating　dislocation　interactions,　multiplication,　and　accumulation.　Wavy　dislocations　form　walls　that　entangle　with　slip　bands,　promoting　strain　hardening　and　delocalizing　plastic　strain.　A　simultaneous　combination　of　high　yield　strength　(1.1　GPa)　and　tensile　strain　to　failure　(28%)　is　achieved;　these　values　are　among　the　best　reported　so　far　for　refractory　high-entropy　alloys.　©　The　Royal　Society　of　Chemistry.