Objective To summarize the acylcarnitine profile in children with malnutrition,with an attempt to distinguish it from those of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency,multiple acylCoA dehydrogenase (MAD) deficiency,or glutaric aciduria type Ⅱ (GA Ⅱ).Methods Thirteen pediatric patients with malnutrition and 214 children of the same age but without malnutrition,which was set as the control group,were included in this study.The blood samples were collected at admission,and the concentration of carnitine and acylcarnitines were measured in bloodspots by tandem mass spectrometry using samples nnderivatized.Results The concentrations of acylcarnitines which were involved in fatty acid oxidation,including octadecanoyl (C18) to acetyl (C2) acylcarnitines and ketonic acylcarnitines,were higher in malnutrition group than in the control group.Particularly,the concentration of decanoyl acylcarnitine (C10) in the malnutrition group was (0.203 ±0.105) μmol/L,which was out of the normal rang (0-0.200 μmol/L),was significantly higher than that [(0.054 ±0.030) μmol/L] in the control group (P ＜0.001).There was no significant difference in the concentrations of acylcarnitines [e.g.propionyl (C3),isovaleryl (C5),3-hydroxy-isovaleryl (C5OH),and glutaryl (C5DC) acylcamitines] involved in amino acid decomposition between the malnutrition and control groups.Conclusions The concentrations of acylcarnitines related to fatty acid oxidation elevate in children with malnutrition.In particular,the medium-chain acylcarnitines C10 is out of the normal range,which can be used to differentiate malnutrition from MCAD and MAD.