The effect of botulinum toxin type A injection on voluntary grip control was examined in a 53-year-old female, who sustained a hemorrhagic right middle cerebral artery stroke 3 years previously, which resulted in finger flexor spasticity and residual weak finger/wrist extension. The patient received 50 units of botulinum toxin type A injection each to the motor points (2 sites/muscle) of the left flexor digitorum superficialis and flexor digitorum profundus, respectively. Botulinum toxin injection led to weakness and tone reduction in the spastic finger flexors, but improved grip release time in grip initiation/release reaction time tasks. Improved release time was accompanied by shortened extensor electromyography activity, and improved release time likely correlated with blocked co-contraction of finger flexors during voluntary finger extension. This case report demonstrated that botulinum toxin injection improved voluntary motor control of the hand in a chronic stroke patient with residual finger extension.