The　secondary　effluent　of　three　WWTPs　was　treated　by　ozonation　to　investigate　organic　biodegradability　enhancement.　The　bulk　experimental　method　was　used.　Ozone　adding　dosage　was　controlled　to　be　2,　4,　6,　8,　10　mg/L　by　adjusting　the　adding　time.　Results　showed,　UV254　and　SUVA(UV254/DOC)decreased　with　the　increasing　of　the　ozone　dosage.　When　ozone　adding　dosage　was　6　mg/L,　UV254　and　SUVA　decreased　about　54.4%　and　56.6%　respectively;　while　BOD5/COD,　BDOC　and　BDOC/DOC　were　improved　above　30%,　360%　and　360%　respectively.　It　could　be　concluded　that　suitable　ozonation　could　improve　the　biodegradation　of　the　organic　substances　in　the　secondary　effluent.　The　organic　substance　was　analyzed　by　the　excitation-emission　matrix　(EEM)　to　investigate　the　variation　regularity　of　organic　matter　changes　of　the　ozoned　and　non-ozoned　secondary　effluent.　The　main　organic　substances　of　the　secondary　effluent　in　the　plant　were　aromatic　protein　like　substances　and　humic　substances,　ozone　could　significantly　remove　these　types　of　organic　substance.