Background and Objectives: To investigate the clinical outcomes in septic patients receiving parenteral fish oil. Methods and Study Design: A prospective, non-randomized, observational clinical study was carried out in 112 patients with sepsis from March, 2013 to May, 2015 in the surgical intensive care unit (SICU) of a tertiary-referral hospital. The patients were put into one of two groups; either the control or the study group. Patients received the standard treatment of sepsis based on guidelines in the control group. In the study group, patients received parenteral nutrition (PN) containing fish oil. The Acute Physiology and Chronic Health Evaluation II (APACHE II) scores, the length of ICU and hospital stay, duration of mechanical ventilation, mortality, and readmission into the ICU were recorded. Tumor necrosis factor (TNF)-α and procalcitonin (PCT) levels were also evaluated. Results: The study group showed a significant reduction for all-cause mortality (20.0% vs 10.0% in study and control groups, p=0.034) and APACHE II score on day 5 (p=0.015), day 7 (p=0.036) and day out of SICU (p= 0.045) compared with the control group. The study group tended to show a shortened length of stay in the ICU compared to the control group. However, TNF-α and PCT level, 28 d mortality, the length of hospital stay and the duration of mechanical ventilation did not show statistical differences between the two groups. There were no drug-related adverse effects shown during the study. Conclusions: PN with fish oil is probably safe and may improve clinical outcome in critical ill patients with sepsis.