To evaluate the efficacy of 125I radioactive seed implantation for locally recurrent rectal cancer (LRRC), and analyze the relationship between the efficacy and dosimetry. From September 2003 to December 2011, 36 patients with locally recurrent rectal cancer received 125I seeds implantation under CT guidance in our center. Each patient underwent three-dimensional treatment planning and dosimetric verification post implantation. The median activity of seed was 0.7 mCi (0.4 to 0.8 mCi), and the median number of seeds was 74 (33 to 137). Overall survival of the patients was calculated and prognostic factors were evaluated. The correlation analysis, log-rank test, and Cox regression analysis between the overall survival, local control and the dosimetry was performed with predictive analytics software. The median overall survival was 16.2 months (95% CI 13.5 ∼ 18.9 months).The median local control time was 10.0 months (95% CI 6.2 ∼ 13.8 months). The V100 was 90.0 ± 0.3%, the D90 was 118.6 ± 25.1 Gy. Analysis using the log-rank test suggested that V100 is correlated to the overall survival time (P = 0.035), D90 is correlated to the local control time (P = 0.048). Cox proportional hazards model suggested that V100 is correlated to the overall survival time (P = 0.044). V100 > 90% and D90 > 140 Gy is beneficial to improve patient survival and the tumor control. CT-guided radioactive seed implantation provides a safe and effective method to control local tumor growth and prolong the survival of patients with locally recurrent rectal cancer. V100 and D90 may predict a favorable patient’s survival and tumor control.