The plasmid pSGL1(7.4 kb) which was isolated from antitumor antibiotic C-1027 producing strain Streptomyces globisporus C-1027 was characterized. It could be introduced into Streptomyces lividans by transformation. Following a series of deletion experiments, the minimal replication region was located within a 2.0 kb Sau 3AI fragment. pSGL1 is compatible with pIJ101. pSGL1 and its derivatives have a copy number of 70-250. Some of the derived plasmids such as pSGLN and pSGLS3 have suitable selectable antibiotic resistance marker and unique restriction endonuclease sites and may be potentially useful as cloning vectors. These plasmids may be used to design and construct efficient secretory expression vectors.