A suture length to wound length ratio (SLWL ratio) of 4:1 for laparotomy closure has proven in clinical studies to reduce incisional hernia incidence. The effect of different SLWL ratios on the mechanical qualities of the healing incision has not been examined experimentally. In 50 rats, the musculo-fascial layer of median laparotomies was closed with polypropylene sutures using SLWL ratios of 8:1, 4:1, 2:1 and 1.7:1. Single and running sutures, different tissue bites and different suture tensions were applied. Five rats served as controls. After 14 days, the horizontal strength of the incision was tested in a digitised tensiometer. The SLWL ratio, suture tension and suture technique proved to have significant influences on the mechanical strength of the incision. Running sutures and especially closures with a ratio of between 4:1 and 8:1 proved significantly stronger than wounds closed with single sutures. When small tissue bites were applied, the positive influence of running sutures was equalised in the early phase of wound healing. High suture tension led to significantly weaker scars independent of the applied suture technique. In accordance with clinical data, it could be proven experimentally that running closure of midline laparotomies with a SLWL ratio above 4:1 avoiding high suture tension exerts a significantly positive effect on the mechanical strength of the incision. Further studies are needed to allow measurement and better control of suture tension.