Objective:　Screening　a　high　and　stable　mutant　strain　from　S.　tenebrarius　Ts-228　for　CTB　(carbamoyltobramycin)　production.　Methods:　A　parent　strain　(Ts-228)　was　isolated　by　natural　selection,　then　treated　by　UV,　and　cultured　on　plate　containing　tobramycin.　Finally,　a　high　yield　mutant　Tt-49　was　obtained　through　several　cyclic　screening.　Its　productivity　was　detected　in　flask　and　the　curves　of　typical　fermentation　were　processed　in　50L　fermenter.　Results:　A　mutant　strain　Tt-49　was　cultured.　Its　fermentation　titre　increased　to　5869u/ml　which　was　1.8　times　higher　than　the　parent　strain　Ts-228,　and　the　component　ratio　of　tobramycin　comes　up　to　68.5%.　The　fermentation　course　of　Tt-49　only　need　4　days.　The　18h-seed　mycelium　and　10%　W/V　of　inoculation　were　used.　Conclusions:　The　combination　of　natural　selection　and　UV　was　a　useful　method　for　tobramycin　from　S.　tenebrarius.　Dissolved　oxygen　is　an　important　parameter　in　fermentation　condition.