Objective To investigate the effect of pregnancy and spontaneous delivery on the morphologic characteristics of the levator ani muscle and innervation of the vaginal mucosa. Methods Eight nullipara without pelvic floor dysfunction (PFD) and 64 normal primipara undergoing spontaneous delivery were enrolled in this study during July to December 2006 in Peking Union Medical College Hospital. Biopsy specimens of levator ani muscle (LAM) and anterior and posterior vaginal walls were obtained from the puerpera as well as from the 8 nullipara undergoing vaginal operation. The structures of LAM were examined with histological techniques. Vaginal mucosa specimens were examined using immunohistochemistry staining for protein gene product 9. 5 ( PGP 9. 5), vasoactive intestinal poptide (VIP) and ne uropeptide Y ( NPY),and the positive stained nerve fibers were calculated respectively. Results The LAMs of the puerpera undergoing spontaneous delivery presented myogenetic and neurogenetic changes, both acute and chronic.Type Ⅰ muscular fibers were predominant(79% )with both types increasing in diameters [ (86±9)μm and (79±15) μm]. Significantly different ( P < 0. 05 ) innervation of PGP 9. 5, VIP, and NPY nerve fiberswas observed between epithelial lamina of anterior vaginal wall(5.9±3. 3, 7. 6±3. 1 and 8. 2±3. 2, respectively) and that of posterior vaginal wall (3. 8±2. 9, 5.9±3. 1 and 6. 0±3.0, respectively), with the nerve fibers being more in epithelial lamina of anterior vaginal wall, while no difference in the innervation of nerve fibers was observed in the lamina propria. Significantly different( P <0. 05 ) innervation of PGP 9. 5 and VIP nerve fibers was observed in the lamina propria of the anterior vaginal wall in puerperal undergoing vaginal delivery (6.9±3.2 and 4.9±2. 1) compared with those in nullipara (3.9±3.6 and 3. 1±1.2). Conclusions Pathologic changes occur in LAMs and pelvic floor nerves during labor and delivery. LAM fibers become hypertrophy to adapt to the physiological changes during pregnancy. Richer innervation of PGP 9. 5 and VIP nerve fibers in the lamina propria of the anterior vaginal wall in puerpera undergoing spontaneous delivery is beneficial for dilation of the blood vessels and smooth muscles and makes preparation for delivery.