An　as-cast　Al0.3CoCrFeNi　high　entropy　alloy　with　face-centered　cubic　(FCC)　structure　was　processed　by　high-pressure　torsion　(HPT)　to　different　strain　values.　This　deformation-induced　microstructure　evolution　was　investigated　by　using　Vickers　hardness,　electron　backscatter　diffraction,　X-ray　diffraction　and　transmission　electron　microscopy.　The　results　show　that,　during　HPT　processing,　the　crystal　structure　is　not　changed,　remaining　FCC　structure,　while　nanocrystallization　of　grains　is　induced　by　HPT　to　30　nm　of　average　grain　size;　grain　refinement　is　achieved　through　twinning　(including　primary　and　secondary　twinning),　de-twinning　(including　primary　and　secondary　de-twinning)　and　twin　boundary　subdivision;　competition　between　twinning　and　de-twinning　processes　contributes　to　the　decrease　and　subsequent　increase　in　twin　boundary　spacing,　while　the　minimum　spacing　of　primary　and　secondary　twins　reach　2.7　nm　and　0.9　nm,　respectively.　©　2015,　Beijing　Institute　of　Aeronautical　Materials　(BIAM).　All　right　reserved.