An instrument-assisted soft tissue mobilization (IASTM) technique has recently been used specifically to inhibit hypertonic muscles and to lengthen muscle fiber shortness. However, it is unknown whether IASTM will show such promising inhibition effects on excessive ankle plantarflexion following stroke. Therefore, the purpose of this study was to use electromyographic (EMG) analysis to determine the ability of IASTM to reduce gastrocnemius (GCM) hypertonicity and concurrently facilitate tibialis anterior (TA) lengthening in a stroke patient. EMG activity on the patient's TA and GCM was measured before and after applying IASTM. After the intervention, the GCM was deactivated by 43%, and TA activity increased by 150%, indicating IASTM-induced inhibition of the overactive GCM. The neuromobilization technique using IASTM showed a promising improvement of neuromuscular imbalance between TA and GCM activations, which can increase gait performance in a stroke case.