The par region of pSC101 was cloned into pUC9, and pEC302 was obtained. The stability of pEC302 and pUC9 in E. coli HB101 was tested on M9 medium to determine the effect of par region on the stability of plasmid. After 40 generations, pUC9 was almost completely lost, while pEC302 was 100% maintained in host cells.