Background and Objectives: The present study was conducted to evaluate the effect of cod skin peptide (CSPE) on chemotherapy-induced toxicity in gastric cancer patients. Methods and Study Design: A cohort of 60 gastric cancer patients for chemotherapy was randomly divided into two groups (n=30 per group), who were orally treat- ed with either supplemental CSPE or placebo apart from chemotherapy. The hematologic and gastrointestinal tox- icities experienced by the patients, as well as their Karnofsky Performance Status (KPS) as an index of quality of life was evaluated. Results: Leukocyte counts and haemoglobin levels were significantly reduced in the group treated with peptide (p<0.05), while gastrointestinal toxicity was not affected (p>0.05). KPS consists of 11 cate- gories of quality of life, and the score denoted in deciles ranges from 100 (asymptomatic, normal function) to 0 (death). The KPS score is used to evaluate a cancer patient’s ability to function at work and home, the severity of symptoms, and the patient’s need for personal and medical care. Treatment with CSPE significantly improved the quality of life of patients, as indicated by increased KPS scores (p<0.05). Conclusions: CSPE can potentially be considered as a food supplement that can be used to improve the quality of life of cancer patients.