The growth of grazed Zoysia japonica plants under a deciduous forest at 3 tree densities was investigated. Z. japonica sods were transplanted in March 1996. The rooting ratios of Z. japonica sods were 75, 86 and 98% under the 3 treatments consisting of low (300 trees/ha), medium (440 trees/ha) and high (630 trees/ha) tree densities (hereafter referred to as “thin, medium and dense treatments”), respectively. The highest rooting ratio recorded under the dense treatment was ascribed to the higher soil water content that was maintained under the dense canopy. Ground coverage of Z. japonica increased in all the treatments in the second and third years after transplanting. The most rapid increase in growth and highest dry weight of Z. japonica were recorded in the thin treatment with 60% coverage and 573 g/m² dry weight in October of the third year. Estimated leaf area index (ELAI) of the trees increased gradually from the first year to the third year in all the treatments. The highest ELAI value was recorded in the dense treatment throughout the experiment. The amount of tree litter decreased from year to year in all the treatments, and no appreciable differences were recognized among the treatments. Therefore, the rooting of transplanted Z. japonica under the tree canopy did not seem to be inhibited by shading within the range of the thinning intensities examined, although the growth of Z. japonica was more rapid under the low density of 300 trees/ha with an average of 9 m height.