Abstract： Objective In this retrospective study, we analyzed the magnetic resonance imaging (MRI)and computed tomography(CT)scans of patients with prostate cancer to investigate the relationship between the apex of prostate and the anatomic structures visible in CT, and to provide evidence for localizing the prostatic apex in radiation treatment planning. Methods MRI and CT scans from 108 patients with prostate cancer were analyzed to measure the distance between the prostatic apex and the bottom of ischial tuberosities,the bottom of obturator foramen, the bottom of pubic symphysis and the bulb of the penis. The volume of prostate was calculated and the relationship between the size of the prostate and the localization of the prostatic apex was analyzed. Results The prostatic apex is located 13. 1 mm ±3. 3 mm superior to the bulb of the penis, 11.0 mm ± 5.4 mm superior to the bottom of obturator foramen, 31.3 mm ± 5.5 mm superior to the bottom of ischial tuberosities, and 7. 1 mm ± 4. 7 mm superior to the bottom of obturator foramen. There was no correlation between the size of prostate and the localization of the prostatic apex(R =0. 07、-0. 33, all P ＞ 0. 05). Conclusions Ninety-five percent of patients had a prostatic apex that is above the bulb of the penis 6 mm, and 100% of patients had a prostatic apex that is above the bottom of obturator foramen.