[Purpose] This study examined whether limited mental practice improves the motor performance of poststroke individuals with hemiparesis. [Subjects] Twenty-three participants with poststroke hemiparesis (40-82 years of age) participated in this study. [Methods] The subjects were divided into four groups with respect to a dart-throwing task: the no-practice, physical practice only, mental practice only, and mental and physical practice groups. The groups were compared in terms of gains in motor performance, mental imagery vividness, and level of concentration during mental practice. [Results] No statistically significant difference was found for gains in motor performance among groups, and there was no correlation between imagery vividness and motor performance gains. However, a correlation was found between gains in motor performance and mental concentration during mental practice. [Conclusion] The results suggested that limited mental practice for individuals with poststroke hemiparesis may not improve motor performance. However, a higher degree of concentration during mental practice may improve motor performance.