Abstract： Objective To investigate the neuromuscular characteristics of the pelvic floor in women with urinary incontinence (UI) during pregnancy and after vaginal delivery and the pathologic characteristics of the levator ani muscle (LAM)and innervation of the vaginal mucosa. Methods From Jul. to Dec. 2006, 100 primiparas presented to Peking Union Medical College Hospital were enrolled, and symptoms of UI were assessed by International Consultation on Incontinence Questionnaire Female Lower Urinary Tract Symptoms Module. After the third stage of labor, biopsies of levator ani muscle (LAM) and anterior and posterior vagina mucoaa were obtained. LAMs's structure were successfully stained in 27 cases for examination of the morphological changes, classification and measurement. Vaginal mucosa specimens were successfully stained in 40 cases with the following immunohistochemistry stainings: PGP9.5, VIP and NPY staining, and the positive stained nerve fibers were calculated respectively. Results The type Ⅰ muscular fibers were predominant(76.5%～79.6%) in LAMs in both UI and non-UI groups and no significant difference was observed in either diameters or ratio of muscular fibers of type Ⅰ or Ⅱ fibers (P>0.05).Innervation of VIP nerve fibers in the lamina propria of the anterior vaginal wall was different between the UI and non-UI group post delivery[(3.7±1.0)/HPE vs (5.2±2.1)/HPE, P<0.05)].Parturients in the UI group had experienced longer duration in the second stage than those in non-UI group [(63.3±25.4) min vs (44.8±23.3) rain, P<0.05]. Prolonged second stage of labor is the risk factor of UI after vaginal delivery (Logistic regression coefficient = 0.028, P< 0.05).Conclusions The changes of morphology, muscular fiber diameters and proportions in LAMs of parturients is directly associated with neither antipartum nor postpartum UI. Decreased innervation of VIP nerve fibers in the lamina propria of the anterior vaginal wall may contribute to the pathogenesis of UI after normal delivery. Prolonged second stage constitutes a risk factor for postpartum UI.