The uterosacral ligaments are thought to contribute to pelvic support. The objective of this study was to compare the structural components of these ligaments in women with and without pelvic organ prolapse (POP). We characterized uterosacral ligaments of 25 postmenopausal women with POP and 16 controls histomorphologically and immunohistochemically by quantifying their content of collagen I, III, and smooth muscle using a computerized image analysis. In 84% the uterosacral ligaments were composed of more than 20% of smooth muscle cells. There was no difference in collagen I expression and smooth muscle cell amount between women with POP and those without. In contrast, the collagen III expression was significantly related to the presence of POP (p<0.001) rather than age or parity. Our findings suggest that the higher collagen III expression might be a typical characteristic of POP patients’ connective tissue. The considerable amount of smooth muscle cells in uterosacral ligaments may provide pelvic support.