It is known that sutures enhance wound closure and promote healing. Sutures initially provide the mechanical strength to seal the wound and protect it from pathogens. Previous studies of suture mechanics focused on the material strength or knotting methods in vitro. Only a few studies have investigated the correlation between the healing strength of wounds and suturing. The purpose of this study was to investigate how the size of 4-0 and 6-0 nylon sutures affect the healing skin strength in rats. The temporal tensile breaking strength and normalized recovery index were measured by tensile testing. The histology observations were also obtained for structural correlation. Our results find that the mechanical strengths of both 4-0 and 6-0 groups do not have a statistical difference in the first two weeks. After four weeks, however, the breaking strengths of healing skin from the thicker 4-0 suture group are higher than the thinner 6-0 suture group. Histological observation showed more inflammatory cells in the 6-0 group than in the 4-0 group in the first week. These results reveal that small sutures can prolong healing time. The histological results are consistent with this finding, which demonstrated more inflammatory cells and extension of the inflammation phase.