This study has analyzed fracture morphology of four nonabsorbable commercially available sutures before and after implantation in rats. Also, tensile and knot strength retention have been evaluated after 3 and 8 weeks in vivo. Scanning electron and optical light microscopes were used for analysis of fracture morphologies and surface changes of the sutures. A clear effect of in vivo on the tensile and knot strength changes, and the fracture mechanism was seen for braided sutures. The suture size was also important for braided sutures, as fibrous tissue formation plays an important role in terms of the size. The fiber's surface properties were also important for the fracture morphology. A smooth and even surface was not suitable for the fibrous tissue formation as seen in monofilament sutures. Therefore, the polymer type was very important for the monofilament sutures, as it was the most important parameter to determine the fracture morphology and was not affected by the implantation and the implantation time. The size of the suture was also important for the polypropylene in terms of axial splitting before and after implantation. This, however, was not the case for knot strength tests. The knot was undone regardless of the size. Surface characteristics were very important for braided sutures, as they have a rough surface that supports tissue formation on the fracture mechanism, tensile and knot strength. Silk suture has single filaments with no regular diameter and smooth surface. Therefore, silk suture has more tissue formation postimplantation compared to polyester suture.