Plasmid-specified traits like lactose metabolism and L-asparginase production could be eliminated from Streptomyces longsporesflavns culture during production of fermented product (Microbial succession). In this study we mainly focus on plasmid profiling and plasmid characterization from S. longsporesflavns isolated from marine soil. Then we observe the efficacy of plasmid curing agent on S. longsporesflavns. Plasmid-free strains and cured derivatives harboring only a single plasmid (6.2 Kbp) were also obtained. Treatment of S. longsporesflavns with novobiocin at concentrations of 2.4 µg/ml could produce a large number of chloramphenicol -variants at a very high frequency (4.6%). These curing data confirmed the novobiocine act as an effective curing agent for S. longsporesflavns.