Abstract: Objective　To introduce a case of ethylmalonic encephalopathy which is an autosomal recessive metabolic disorder caused by mutations in the ETHE1 gene. Methods The clinical course and gene mutation in a case of ethylmalonic encephalopathy was retrospectively analysed. Results A previously healthy girl presented with intractable diarrhea from the age of 7 months. Since then, progressive psychomotor regression has been observed. When she was 23 months, her blood butyrylcarnitine was significantly increased (4.48 μmol/L vs. normal range 0.0~1.0 μmol/L), and isovalerylcarnitine (0.70 μmol/L vs. normal range 0.0~0.65 μmol/L) was also elevated. Her urine levels of ethylmalonic acid and methylsuccinate acid were markedly increased. Cranial MRI revealed bilateral basal ganglia lesions supporting the diagnosis of ethylmalonic encephalopathy. On her ETHE1 gene, a reported mutation (c.488G>A, p.R163Q) and a novel mutation (c.203T>C, p.L68P) were identified. After lactose-free dietary treatment and the supplements of L-carnitine, coenzyme Q10, vitamins B1, B2 and C, gradual improvement in general condition, intelligence and motor development has been observed. Conclusions Ethylmalonic aciduria is common in the patients with inborn errors of mitochondrial fatty acid beta-oxidation. In ethylmalonic encephalopathy, elevated blood levels of butyrylcarnitine and isovalerylcarnitine are common and ETHE1 sequencing is helpful in its diagnosis.