The high-level expression plasmid for streptokinase, pSK100, has been constructed. It contains a tac promoter, an ompA signal sequence, a streptokinase structural gene(skc) and a rrnBT1T2 transcription terminator. E. coli JM109 carrying pSK100 produced about 5,000IU of streptokinase per 1 mi of LB-ampicillin media. About 95% of the expressed streptokinase was secreted into the periplasmic and extracellular fractions. The recombinant streptokinase in high yield and purity may be a potential alternative source for the therapeutic agent.