Abstract: Objective To compare the influence of changes of bladder volume on biological dosage capacity of the normal organs in three dimensional conformal brachytherapy for vaginal stump. Methods A total of 15 gynecological tumors patients were included in this study, and were given three dimensional conformal brachytherapy in vaginal stump. During three-dimensional conformal brachytherapy, the bladder was emptied and infused by saline at a dosage of 50, 100 and 150 mL, respectively. The values of the dose of 2 cm³ of normal organ closest to the radiation source(D_{2 cm³})of small intestine, rectum, bladder and sigmoid colon were compared at different bladder volumes. Results The D_{2 cm³} of small intestine in emptying was higher than 50, 100 and 150 mL saline(P<0.01). The change of bladder volume had no significant effect on values of D_{2 cm³} of rectum, bladder, and sigmoid colon. Conclusion The changes of bladder volume have an impact on D_{2 cm³} of the small intestine, but no influence on the D_{2 cm³} of rectum, sigmoid and bladder. For retrofitting of the vaginal stump, bladder filling of 50 mL is appropriate, which can reduce the dosage of small intestine.