BACKGROUND: Approximately, 6-31% of nutritional deficits are present before the stroke and worsen during hospitalization. Besides affecting the patient’s physical and mental abilities, stroke can also cause a decrease in nutritional status, which has a major influence on the rate of death and disability. One intervention to overcome stroke patients’ nutritional problems is giving oral nutritional supplementation. The role of oral nutritional supplementation in stroke severity in patients with acute ischemic stroke has not yet been extensively studied. AIM: This study aimed to evaluate the effect of oral nutritional supplementation on the National Institute of Health Stroke Scale (NIHSS) in patients with acute ischemic stroke. METHODS: This was an experimental study with a pre- and post-study group method. Twenty-eight patients with acute ischemic stroke were referred to Adam Malik General Hospital, Medan, Indonesia, and were allocated randomly into two groups. Fourteen patients as control group received the normal hospital diet and 14 patients as intervention group received normal hospital diet plus oral nutritional supplementation for 7 days. The NIHSS scores were assessed on the first day and the eighth day after intervention in each group. RESULTS: There were significant reductions in NIHSS scores between day 1 and day 8 in both groups (p < 0.001). The mean delta NIHSS scores were −2.28 ± 1.63 and −2.57 ± 1.98 in the intervention and control groups, respectively. There was no significant difference in NIHSS scores between the intervention and control groups (p = 0.682). CONCLUSION: The effect of oral nutritional supplementation significantly reduced the NIHSS scores in acute ischemic stroke, but there was no significant difference compared to the normal hospital diet.