Effects of pulsing electromagnetic fields (PEMFs) on ligament healing were investigated using 80 rabbits. All animals received square resection (4 mm x 4 mm) of both patellar ligaments in full thickness at their center. They were divided into 4 groups of 20 rabbits each and stimulated with different electromagnetic intensity of 0 (control), 2, 10, and 50 gauss (G) for 6 hr daily. Pulse frequency and pulse width were 10 Hz and 25 microseconds, respectively. After PEMFs stimulations for 1, 2, 3 and 4 weeks, 5 animals of each group were euthanized and the regenerated tissue at the defective portion was investigated histologically and biomechanically. Histologically, the tissue stimulated by PEMFs showed an earlier increase in capillaries and fibroblasts and more matured, prominent longitudinal orientation of collagen fibers than those of control groups. Among the rabbits stimulated electromagnetically, those stimulated at 50 G revealed the earliest ligament healing. Tensile strength of regenerated ligament tissues of any PEMFs groups increased significantly at 1 and 2 weeks after operation, however, at 3 and 4 weeks after operation, there were no significant differences between groups. Among these values, those of 50 G group were the highest consistently during most of the experimental period. From the above results, PEMFs enhanced the earlier stage of ligament healings and 50 G gauss seemed to be the most effective among the 3 field intensities used. This promoting effect may potentiate the earlier recovery of the function after the ligament injury.