A randomised trial was carried out to determine the effect of supplementation of fish oil among 51 children with leukaemia aged 4 to 12 years on appetite level, caloric intake, body weight and lean body mass. They were randomly allocated into the trial group (TG) and the control group (CG). At baseline, 30.8% of TG subjects and 44.0% of CG subjects were malnourished and 7.7% of subject from TG and 28.0% from CG were classified as stunted. The majority of subjects from TG and CG were in the mild malnutrition category for mid upper arm muscle circumference (MUAMC)-for-age. The TG group showed significant increment in MUAMC (0.13 cm vs -0.09 cm) compared with CG at 8 weeks (p<0.001). There was a significant higher increase for appetite level (0.12±0.33) (p<0.05) and an increasing trend on energy and protein intake in the TG group (213±554 kcal; 3.64 ±26.8 g) than in the CG group. In conclusion, supplementation of fish oil has a positive effect on appetite level, caloric intake and MUAMC among children with leukaemia.