We monitored the response of tissues to mechanical wounding, and changes of moisture content of common horse chestnut (Aesculus hippocastanum L.). Branches were wounded by drilling a hole with a diameter of 3 mm through the complete diameter using the battery-powered drill. All branches were wounded on April 8, 2010. The wounded segments of branches were examined by 3D MR imaging, performed in weekly intervals. Immediately after the mechanical wounding, the 3D MR imaging revealed a dehydration of tissues in the immediate vicinity of the wound. During 7th and 14th day the tissue under the dehydrated bark was moistened. During 14th and 28th day a tissue with increased moisture content appeared in the pith area. Wound wood was detected around the wound. Progressive cambium and bark necrosis, as well the dehydration and necrosis of the part of the tissue near the wound, was detected on 35th day. The occurrence of callus was also visible. The moist layer in the interior disappeared. On 49th day the wound tissue started to overgrow the wound. An extensive occurrence of wound tissues, and consequently the overgrowth of the wound in the transverse direction, were detected on 56th day. Here, the moisture reaction zone did not occur.