This study was conducted to investigate the effects of unaffected-side active treatment on the gait of hemiplegic patients. The study subjects were 20 patients who showed hemiplegic symptoms after a stroke. Through a random classification method, the subjects were divided into an experimental group (n = 10) who underwent treadmill exercise based on the concept of unaffected-side active treatment to strengthen the paretic side lower extremity after proprioceptive neuromuscular facilitation (PNF) treatment and a control group (n = 10) who underwent general treadmill training without unaffected side-active treatment after PNF treatment. The therapeutic interventions were performed three times a week for 4 weeks. To analyze behavioural motor motions, the patient's gait speeds and ankle angles were measured using the timed up-and-go (TUG) and the Dartfish program before treatment and 14 and 28 days after beginning treatment. The study results showed that the TUG and ankle angles significantly differed between the experimental and control groups at 14 and 28 days after beginning treatment. These significant differences between the two groups were verified. In conclusion, a lower limb strengthening treadmill exercise based on unaffected-side active treatment can increase gait speed and ankle angle by improving motor control ability