Preoperative radiation is associated with an increased risk of wound complications. However, the influences of radiation on musculofascial wound healing remains unclear. The purpose of the study was to investigate the short-term effects of preoperative local radiation on the musculofascial healing of laparotomy incisions in a rat model. Eighteen Fischer 344 rats received radiation doses of 0, 10, or 20 Gy to the abdominal wall and underwent laparotomy 4 weeks later. Two weeks after laparotomy, samples of irradiated muscle were harvested for mechanical tests, histological (Hematoxylin & Eosin, and Masson's Trichrome) and immunohistochemical analyses using KI67, CD31, TGF-β, and MYOD1 antibodies. The elastic modulus (EM), maximum strain (MS), and ultimate tensile strength (UTS) in the 20-Gy group were significantly weaker than those in the 0-Gy group. The EM and UTS in the 20-Gy group were significantly lower than those in the 10-Gy group. The UTS and MS in the 10-Gy group were significantly lower than those in the 0-Gy group. The mean number of inflammatory cells per mm2 in the 20-Gy group was significantly larger than those in the 10- and 0-Gy groups. The mean numbers of CD31-, KI67-, and MYOD1-positive cells, the optical density of TGF-β, and the microvessel density in the 20-Gy group were significantly smaller than those in the 10- and 0-Gy groups. These results indicated that radiation delays musculofascial healing and decreases mechanical strength of the laparotomy incision by creating a chronic inflammatory environment, inhibiting cell proliferation, angiogenesis, granulation maturation, collagen deposition, and muscular regeneration in a dose-dependent manner. The impaired biomechanical, histological and molecular properties may be associated with the higher risk of wound complications in patients who undergo radiotherapy prior to laparotomy.