Purpose: We designed a prospective study to evaluate the effects of total mesorectal excision and autonomic nerve preservation(TME-ANP) on postoperative genitourinary function in the course of time and the quantitative effects of various peri-operative risk factors on the postoperative genitourinary dysfunction. Materials and Methods: Forty-five patients who underwent TME-ANP with rectal cancer were prospectively examined before and after operation, as well after the first, third and sixth postoperative month. The preoperative urological evaluation consisted of International Prostate Symptom Score(IPSS), Erectile Function Domain score in International Index of Erectile Function(IIEF-EFD), Ejaculation domain in Male Sexual Health Questionnaire(MSHQ-EjD) and urodynamic study. Results: Preoperative IPSS decreased significantly in postoperative 1 month. But there was no difference between preoperative IPSS and postoperative IPSS after 3 month of operation. Erectile function significantly decreased in the course of time(p-trend＜0.05). Ejaculation function also significantly decreased after 1 month of operation, however no significant change of MSHQ-EjD was observed thereafter. Multivariate analysis revealed history of abdominoperineal resection and baseline mild erectile dysfunction were found to be the risk factors of decreasing erectile function. Diabetes was associated with diminishing ejaculatory function. Conclusions: While the voiding dysfuncion was no longer problematic following TME-ANP, substantial number of sexual dysfunction persisted despite TME-ANP.