Reconstruction of the anterior cruciate ligament (ACL) with patellar tendon (PT) is a common procedure of the symptomatic ACL-deficient knee. Questions regarding graft incorporation, viability, and nutrition of the transplanted tissure are of concern. This relateds to the graft response to its new intrasynovial milieu and its physical forces. These factors were studied in a 10kg, 5 Mongrel dogs using PT and were evaluated with light microscope and electromicroscope. The follwing results were obtained: 1. Many differecnce were demonstrated between ligament and tendon in its crimp patterns, number of fibrocyte and shape of cell. 2. Transplants from the 2 weeks period, the transplant showed the normal PT crimp but no fibroblasts were seen centally. However, round to ovoid cells were visible on peripheral margin of the thransplant. 3. Transplant from 6 weeks period, the transplant showed ACL like crimp pattern in some section and cellularity was greater than normal PT and cell shape were very similar to native ACL predominated. 4. Transplant from 3 months period, there were no differences from 6 weeks findings.