A　17β-estradiol　(E2)　degrading　strain　was　isolated　by　using　enrichment　culture　of　activated　sludge　from　wastewater　treatment　plants　and　identified　as　the　genus　Dyella.　The　estradiol　degradation　by　this　strain　fitted　in　a　first-order　reaction.　The　degradation　rate　constant　K　was　0.025　h-1.　Methanol　and　sodium　acetate　could　be　utilized　by　the　bacteria.　In　contrast,　ethanol　and　glucose　were　not　completely　utilized　within　10　days.　Estradiol　was　converted　to　estrone　first　and　then　used　for　further　degradation.　Estrone　degradation　by　the　bacteria　also　fitted　in　a　first-order　reaction　(K=0.0133　h-1).　The　relationship　between　the　specific　degradation　rate　and　substrate　concentration　fitted　in　the　Monod　equation.