The uterosacral ligaments are an important part of the pelvic support system. The objective of this study was to compare the expression of collagen type I and collagen type III in the uterosacral ligament biopsies from women with and without pelvic organ prolapse (POP). The uterosacral ligament biopsies were obtained from women with POP (n = 29) and non-POP subjects (n = 35). Immunohistochemistry for collagen type I and collagen type III was performed on formalin-fixed and paraffin-embedded sections. The two groups were matched for age, body mass index, parity and postmenopausal status. The expression of collagen type I (p < 0.001) and collagen type III (p < 0.0001) differed between women with POP and non-POP subjects. There was decreased expression of collagen type I and increased expression of collagen type III in uterosacral ligaments of women with POP compared with non-POP subjects. This difference indicates a possible relationship between POP and the immunohistochemical expression of collagen type I and collagen type III in uterosacral ligaments.