Gait parameters and gross motor function improve after 12 sessions of small-sized Hybrid Assistive Limb® (S-HAL) training in adult cerebral palsy (CP) patients. However, there are no reports on repetitive robot-assisted gait training using the newly developed very small-sized HAL (2S-HAL). This study aimed to examine the effect of using 2S-HAL on a pediatric CP patient.The subject was an 11-year-old boy (height = 138 cm, weight = 30 kg) with spastic quadriplegia due to periventricular leukomalacia, with Gross Motor Function Classification System level IV. HAL training was performed for 2-4 sessions/week for 20 min/session (i.e., 4-week period with 12 sessions). Outcome measures were walking ability, gross motor function, Canadian Occupational Performance Measure (COPM), and Pediatric Evaluation of Disability Inventory measured before, after, and at 1, 2, and 3 months after HAL-assisted gait training.After HAL intervention, gait speed, step length, cadence, 6-min walking distance (6MD), Gross Motor Function Measure (GMFM), and COPM increased and physiological cost index (PCI) declined compared to those before intervention. The peaks of gait speed, step length, and cadence were 2 month, 1 month, and 3 month, respectively. 6MD, PCI, and GMFM at 1-3 months post-intervention were maintained. COPM peaked at 1 month post-intervention but remained higher than that before intervention.This is the first report of repetitive intervention using 2S-HAL in a pediatric CP patient. Gait training using 2S-HAL may be effective in CP patients as it improves post-training walking ability and gross motor function.