The purpose of this study was to investigate whether a sustained grip strength test is workable as an accurate assessment of activity limitation related to muscle weakness of the paretic hands of stroke patients with mild pareses. Sixty-one stroke patients with mild pareses participated in this study. The maximal grip strength and an ability to sustain grip strength were examined with the Sustained Grip Strength Test. The latter ability was measured by the sustained period of the maximal grip strength (a period that exhibited more than 80% of the peak force during a six-seconds trial). The activity limitation of squeezing an object was evaluated in four ADL tasks, and the difficulties were rated according to three scores. We found that there was a significant positive relationship between the degree of the task difficulty and the maximal grip strength for paretic hands whose sustained period was over three sec, in all four assessments (p < 0.05). However, for paretic hands whose sustained period was under three sec, no such relationship was found. Consequently, measuring both the maximal grip strength and the sustained period was needed to assess accurately an activity limitation related to muscle weakness of the paretic hands of stroke patients with mild pareses.