Abstract: A extracellular plasmin producing moderately Acidophilic actinomycetes named YY21 was reported in this paper. On the GYM and PDA medium this strain could growth substrate mycelium and aerial hyphae,and aerial hyphae differentiate into wave-like spore-bearing mycelium which could produce spherical spores. The suitable pH range for the growth of the strain YY21 was 3~7. This strain could secrete protease and amylase,but no extracellular cellulase,and could break down the sulfur amino acid to roduce hydrogen sulfide. It could utilize glucose and raffinose as a carbon source. After this strain was cultured in liquid medium for 3 days,the medium had significant inhibitory effect on the E. coli,and the inhibition zone diameter reached 36.2mm. The medium contain plasminogen and the dissolved circle area was 99.37mm2 on the fibrin tablet.