Background: Disease-related malnutrition exerts adverse effects on the treatment process. This problem can increase infection, inflammatory factors, oxidative stress, recovery delay, length of hospital stay, hospital costs, and mortality, especially in the elderly and patients with malignant diseases admitted to intensive care units. Alpha Lipoic Acid (ALA) is an eight-carbon sulfur-containing compound with antioxidant properties which may be suitable for these patients. The present study aimed to investigate the effects of ALA supplementation on malnutrition, oxidative stress, length of hospital stay, and length of ventilator connection. Methods: This study was a randomized, double-blind, placebo-controlled clinical trial in which 80 patients (18-80 years) were randomly assigned to two groups, including intervention and control groups. The intervention group received ALA (600 mg daily) and the control group received a placebo for 8 weeks. Antioxidant capacity (TAC), malnutrition, waist circumference, arm circumference (MAC), the thickness of skin fat (TSF) were measured before and after the intervention. The present study was performed in the general and neurosurgical ward of Loghman Hakim Hospital affiliated to Shahid Beheshti University of Tehran. Dietary data were assessed using N4 software and statistical analysis was performed using SPSS software (version 20). Quantitative data were considered as mean± SD. A p-value less than 0. 05 was considered statistically significant. Findings: The intervention and placebo groups were comparable in terms of initial characteristics (P<0. 05). Nonetheless, after the intervention, significant changes were observed in TAC (P=0. 538), TSF (P=0. 350), malnutrition (P=0. 184), MAC (P=0. 525), waist circumference (P=0. 343), and length of stay (P=0. 343). There was no difference between the two groups regarding mechanical ventilation time (P=0. 094). Conclusion: As evidenced by the obtained results, 8-week supplementation with 600 mg ALA exerted no significant effect on TAC, malnutrition, waist circumference, MAC, TSF, mechanical ventilation time, and length of hospital stay in ICU patients.