The purpose of this study was to examine properties and sex differences of the decreasing force during sustained isometric grip using various target forces, 50%, 75%, and 100% of maximal voluntary contraction (MVC), for 6 min. Participants were healthy, 15 men (height = 172.9 ± 4.6 cm, body mass = 67.7 ± 5.36 kg) and 15 women (height = 160.9 ±5.4 cm, body mass = 55.9 ± 5.36 kg). The force decrease for target forces of 75% and 100% MVC was marked until 60 sec. from the onset of grip and then decreased gradually. On the other hand, the target force of 50% MVC was maintained for about 60 sec. and then decreased markedly until 100 sec. Differences in the decreasing force among target force levels was observed until 60 sec., and there were no significant differences of the time to decay to 20%, 30%, and 40% MVC. Namely, the time and force exertion reaching an almost steady state were considered to be almost the same at any target force. A sex difference on a parameter was found after 60 sec. or a decreasing force after 40% MVC, and women held it longer or higher than the men. However, the tendency was smaller in the latter phase of the steady state.