ObjectiveTo explore the influence of different radiation doses of 125Ⅰseed on human poorly differentiated gastric cancer cells (BGC823). MethodsSixty four male nude mice of BLAB nu/nu inoculated with human poorly differentiated gastric cancer cells (BGC823) were took as animal models. When tumors of nude mice grew to 0.7-1.2 cm, the nude mice were randomly divided into blank control group, low dose group, middle dose group, and high dose group (n=16). The tumors of nude mice in blank control group were implanted with blank seed, but tumors of nude mice in low dose group, middle dose group, and high dose group were implanted with 125Ⅰseed (the radiation doses of 3 groups were 1.48×10-7 Bq, 2.22×10-7 Bq, and 2.96×10-7 Bq respectively). Four nude mice of 4 groups were randomly collected to measure the tumor volume and weight before implantation, and on 7, 14, 21, and 28 days after implantation, but apoptosis rates and expression levels of cyclinE mRNA were measured on 14 days and 28 days after implantation, by using flow cytometer and semi quantitative RT-PCR method respectively. Results①Except for the blank control group, the tumor volume and weight decreased over time in low dose group, middle dose group, and high dose group. The tumor volume and weight in blank control group were higher than those of other 3 groups on 7, 14, 21, and 28 days after implantation (P < 0.05);in addition, on 28 days after implantation, tumor volume and weight in low dose group were lower than those of middle dose group and high dose group (P < 0.05).②On 14 days and 28 days after implantation, the apoptosis rates of blank control group were lower than those of other 3 groups (P < 0.05), but expression levels of cyclinE mRNA were all higher than those of other 3 groups (P < 0.05). In addition, on 28 days after implantation, apoptosis rate of low dose group was higher than both of middle dose group and high dose group (P < 0.05), but expression level of cyclinE mRNA was lower (P < 0.05). Compared with 14 days in the same group, except for the blank control group (P > 0.05), the apoptosis rates in other 3 groups on 28 days were higher (P < 0.05), with the lower expression levels of cyclinE mRNA (P < 0.05). Conclusions125Ⅰseed in organizational implantation can effectively inhibit the expression of cyclinE mRNA and the growth of human poorly differentiated gastric cancer tissue. Compared with doses of 2.22×10-7 Bq and 2.96×10-7 Bq of 125Ⅰ, low dose (1.48×10-7 Bq) contributes to the apoptosis of human poorly differentiated gastric cancer cells (BGC823).