A　novel　mixotrophic　denitrification　biofilter　for　nitrate　removal　using　polycaprolactone　and　thiosulfate　(MD-PT)　as　electron　donors　was　investigated.　MD-PT　achieved　high　nitrate　removal　efficiency　of　approximately　99.8　%.　The　nitrate　removal　rates　of　MD-PT　reached　1820　g　N/m3/d,　which　was　304　g　N/m3/d　higher　than　that　of　autotrophic　denitrification　biofilter　using　thiosulfate　(AD-T).　Autotrophic　and　heterotrophic　denitrification　pathways　in　MD-PT　were　responsible　for　67.6-94.5　%　and　4.7-32.4　%　of　the　nitrate　removal,　respectively.　The　production　of　SO4　2-　in　MD-PT　was　lower　than　that　in　AD-T,　and　the　effluent　pH　was　maintained　at　approximately　7.3　without　acid-base　neutralization.　The　abundance　of　key　genes　involved　in　carbon,　nitrogen,　and　sulfur　transformation　was　enhanced,　which　improved　the　nitrate　removal　of　MD-PT.　Alicycliphilus　and　Simplicispira　related　to　organic　compounds　degradation　were　enriched　after　the　addition　of　polycaprolactone.　This　research　provided　new　insights　into　mixotrophic　denitrification　systems.