To improve blast resistance of the rice cytoplasmic male sterile(CMS) line Jin23A and its maintainer Jin23B, the indica rice line 75-1-127 carrying a broad-spectrum and durable blast resistance gene Pi9 was used as the donor parent, and Jin 23B and Jin 23A were used as the acceptor parents, a co-dominant marker, CoInDF1R2, was developed according to Pi9 sequence , then was employed in marker-assisted selection breeding practice. Greenhouse inoculation assay was performed using twenty-five Magnaporthe oryzae isolates collected from different rice areas. The results showed that the Pi9 gene donor rice line 75-1-127 showed much higher resistance frequency(92%) than those of two acceptor parents Jin23A and Jin23B(28%). Accordingly, 75-1-127 showed high-level seedling blast resistance but highly susceptible for the receptors in natural nursery. CoInDF1R2 showed clear and stable co-dominant polymorphism between the donor and acceptor parents, amplifying a 354 bp DNA band from genome of 75-1-127, while the PCR product from either genome of Jin23A or Jin23B was about 470 bp. An improved CMS line Jin23A-Pi9 and the corresponding maintainer Jin23B-Pi9 were created through consecutive backcross breeding practice by marker-assisted selection of the CoInDF1R2 marker. Then, Jin23A-Pi9-1 and Jin23B-Pi9-1 were screened as the goal CMS line and maintainer. This study had set the stage for developing elite hybrid rice varieties with superior blast resistance using the three-line method of heterosis utilization.