Zoysia japonica Steud. is unique among Japanese native grasses due to its adaptation for grazing and has been re-evaluated by smallholders of beef calf production in Japan, because of its sustainability without any fertilizer. The relationship between stocking density and herbage production is a key factor for the sustainable management of grazing pastures. Moreover, net primary productivity including both above- and below-ground parts is a parameter used to quantify the net carbon absorption rate by living plants. Generally, stocking density levels affect plant production of pastures. Therefore, to determine the impact of defoliation intensity on net primary productivity of a Z. japonica-dominated pasture, the plant mass including below-ground parts was determined for three years under the stocking densities averaging 3.9, 2.7 and 1.6 animal units ha^-1 y^-1 at the start of the grazing season under set-grazing of beef cattle from June to September. The net primary productivity ranged from 291 to 421 g DM m^-2 y^-1 for above-ground (ANPP) and from -38 to 51 g DM m^-2 y^-1 for below-ground parts. The ANPP was found to be affected by defoliation intensity, defined as the ratio of ANPP that was grazed, and attained a maximum when the defoliation intensity was about 40%. As for cattle performance, they maintained their weight during the grazing season below 35% of annual defoliation intensity.