Ba0.5Sr0.5Co0.8Fe0.2O3-delta　(BSCF)　is　an　excellent　mixed　ion/electron　conducting　cathode　among　solid　oxide　fuel　cells;　however,　its　electrochemical　activity　is　limited　by　the　sluggish　oxygen　surface　exchange.　The　application　range　of　the　BSCF　cathode　can　be　widened　by　preparing　BSCF　in　the　form　of　an　ultrafine　powder;　however,　retaining　the　microstructure　of　the　powder　in　the　cathode　is　challenging　owing　to　the　sintering　of　cathodes　at　high　temperatures.　In　this　study,　we　report　a　combined　modification　and　direct　assembly　approach　for　the　fabrication　of　an　ultrafine,　multi-phase　BSCF-based　cathode.　This　novel　BSCF　cathode　powder　is　first　modified　by　immersing　the　pre-synthesised　micron-sized　BSCF　perovskite　powder　in　a　weakly　acidic　chelating　solution.　The　modification　treatment　changes　the　composition　of　the　powder　and　results　in　the　formation　of　an　ultrafine　microstructure.　The　ultrafine　microstructure　of　the　powder　is　further　retained　in　the　cathode　by　direct　assembly　without　high-temperature　sintering.　The　peak　power　density　of　the　ultrafine,　multi-phase　BSCF　cell　is　1.25　W　cm(-2)　at　750　degrees　C,　much　higher　than　the　0.83　W　cm(-2)　of　the　pristine　BSCF　cell.　This　study　provides　insights　into　the　facile　fabrication　and　application　of　ultrafine　cathodes　for　efficient　solid　oxide　fuel　cells.