Objective To investigate the changes of composition and level of serum free fatty acid (FFA)of children with critical illness.Methods The serum FFAs were measured by gas chromatography in 61 children(27 critically ill eases and 34 healthy controls).The changes in serum FFA was compared between healthy children and critically ill cases.We also evaluated the difference between the data before treatment and those after recovery in children with critical illness.Results Levels of palmitic acid,palmitoleic acid.oleic acid,docosanoic acid.arachidonic acid(AA)and eicosapentaenoic acid(EPA)were evidently higher in the critically ill children than those of healthy control(P＜0.05);children underthe recovery stage showed higher levels of myristic acid,palmitic acid,palmitoleic acid,oleic acid,arechidic acid as compared with healthy controis(P＜0.05).Conclusion Compexed with healthy children,the profile of serum FFA was quite different in critically ill and recovery ones.Critical illness may influence the profile of serum FFA.