Objective To study the effects of vaginal delivery on the biomechanical properties of uterosacral ligaments (USLs) and cardinal ligaments (CLs) and to further explore the effects of vaginal delivery on pelvic organ prolapse (POP). Methods Adult sows (five parous and five nulliparous) were selected as animal models. The passive mechanical behavior of USLs and CLs in vitro was determined using uniaxial tensile experiments, and the effects of delivery on the biomechanical properties of USLs and CLs were analyzed. Results The passive mechanical behavior of the sow uterine ligaments was nonlinear. Regardless of delivery, the maximum stress of the right USLs was greater than that of the left USLs (P<0.05). After delivery, the mechanical properties of the right and left USLs differed significantly. The maximum stress of the left CLs in nulliparous sows was slightly greater than that of the right CLs (P<0.05), and the difference between the left and right CLs was reduced after delivery (P>0.05). The maximum stress of USLs was greater than that of CLs, indicating that USLs could be subjected to more tension than CLs and that USLs played a key role in POP. Conclusions This study provides a reference for understanding the mechanical properties of USLs and CLs, guidance for the development of better treatments such as reconstructive POP surgery, and a theoretical basis for preventing POP.