Objective To explore the change of complications and inflammatory mediators in patients at nutritional risk after intervention with fish oil after major abdominal surgery.Methods Totally 60 patients who had received extrahepatic bile duct exploration ± left lobectomy and radical surgeries for their gastrointestinal tumors in our department from September 2010 to March 2011 were enrolled in this study.Their Nutritional Risk Screening 2002 scores were ≥3 points the day after surgery.These 60 cases patients were randomly divided into fish oil group (n =30) and the control group (n =30).Both groups were treated with total parenteral nutrition isocaloric and isonitrogenous energy emulsion intralipid of 3 Ls' bags after surgery.Aslo,they were treated with electrolyte,vitamins and trace elements equally,which were adjusted according to laboratory tests.The application of parenteral nutrition was no less than 5 days,and the other treatment was provided routinely.Surgeries were performed under general anesthesia in all patients.Urinary catheter was uniformly placed preoperative,and was removed within 24 hours after surgery.The degree of surgical trauma was scored on the operative day.Fasting venous blood samples were collected for measuring the fasting interleukin (IL)-6 and tumour necrosis factor-α (TNF-α) one day before surgery and one and six days after surgery.The relevant complications were recorded.Two patients in the fish oil group withdrew from the study on the third post-operative day.Results TheIL-6 levels were (10.65 ± 4.24),(29.45 ± 9.39),and (13.37 ± 6.99) ng/Land the TNF-α levels were (2.47 ± 1.16),(23.05 ± 11.43),and (6.05 ± 2.97) ng/L in the fish oil group one day before surgery and one and six days after surgery.In the control group,in contrast,the IL-6 levels were (11.17 ± 4.67),(25.10 ± 10.13),and (17.38 ± 7.13) ng/L and the TNF-α levels were (2.70 ± 1.63),(22.11 ± 12.54),and (8.93 ± 3.61) ng/L at the corresponding time points.Comparisons of the IL-6 and TNF-α between the fish oil group and control group showed no significant difference one day before surgery and one day after surgery (P =0.787,P =0.206,P =0.983,P =0.852).Comparison of the IL-6 between the one day and six days after surgery also had no statistical significance (P =0.101).However,the decrease of IL-6 was significantly larger in the fish oil group than in the control group from day 1 to day 6 after surgery (P =0.036).The post-operative levels of TNF-α were significantly different between these two groups (P =0.024).Complications were noted in 3 cases (2 cases of infectious complications) in the fish oil group and in 6 cases in the control group (5 cases of infectious complications) (P =0.002),in which the inffectious complications were also statistically significant (P =0.001).Conclusions Patients at nutritional risks after major abdominal surgeries have higher TNF-α and IL-6 levels.Fish oil can notably reduce the TNF-α level in these patients.In addition,fish oil decreases the surgical complications,in particular the infectious complications.