The　culture　characteristics　of　Streptomuyces　tenebrarius　which　closely　related　to　the　culture　degeneraton　including　changing　to　a　light　yellow　of　colony　color,　preservation　time　and　the　relationship　between　them　were　studied.　To　isolate　high　tobramycin　producing　strains,　multiple　mutagens　such　as　NTG,　NaNO2　and　5-Bu　(5-bromouracil),　as　well　as　the　combined　action　of　UV　treatment　were　used.　It　reveales　that　the　moderate　UV　radiation　treatment　was　the　best　way　to　culture　rejuvenation.　In　order　to　further　increase　the　potency　of　the　strain,　a　measure　of　enrichment　of　high-quality　spores　called　complex　rational　screening　method　which　included　steps　such　as　protopast　fusion,　agar-block　and　solid-state　micro-fermentation　was　used.　A　new　strain　which　has　2.5　times　higher　potency　than　the　parent　strain　with　increasing　tobramycin　component　from　52%　to　71%　was　isolated　in　flasks.