BACKGROUND: Patients with chronic stroke have reduced capacity for performing activities of daily living (ADLs) and are at increased risk for falls during walking due to long-term changes to muscle tone and force, as well as movement control. RESEARCH QUESTION: To investigate the efficacy of lateral stair walking training on muscle strength of affected lower extremities, balance, ADLs, and gait ability in patients with chronic stroke. METHODS: The experimental group received 15 min of lateral stair walking exercise along with 15 min of traditional physiotherapy, whereas the control group received only traditional physiotherapy for 30 min. Both groups received the intervention once a week for 12 weeks. Outcome measurements included muscle strength, postural assessment scale for stroke patients (PASS), Fugal-Meyer assessment for lower extremity (FMA-LE), Barthel index (BI), timed up and go test (TUG), and the gait parameters which were determined by the Reha-Watch system. RESULTS: A total of 24 participants completed the study. The experimental group showed significant improvements in hip extensor, flexor, and abductor strength of the affected limb, FMA-LE, BI, TUG, and gait parameters of stride length, velocity, and cadence. Significant differences in affected limb ankle plantar strength (p = 0.024), PASS (p = 0.017), BI (p = 0.039), TUG (p = 0.049), and gait velocity (p < 0.001) were observed between the 2 groups. SIGNIFICANCE: Lateral stair walking training alongside physical therapy resulted in significant improvements in hip muscle strength and gait parameters in patients with chronic stroke. Our results support the incorporation of lateral stair walking training into clinical rehabilitation programs. Lateral stair walking training in patients with chronic stroke can be used as an effective treatment to improve gait, balance performance, and ADLs.