Abstract: 　Objective　To explore the clinical features of methylmalonic acidemia (MMA) in children admitted to the pediatric intensive care unit, to help improve our understanding of MMA. Methods　The clinical data of 21 patients with MMA admitted to our PICU from December 2012 to August 2016 were analyzed. Diagnosis were confirmed by gas chromatographymass spectrometry, GC/MS. Results　twenty-four of 158 suspected cases were confirmed as having organic acidemia diseases including 21 cases of MMA, one case of propionic acidemia, one case of urea cycle disorders, and one case of glutaric acidemia. The main clinical manifestations were feeding difficulty, malnutrition (13 cases), developmental retardation (12 cases), lethargy (10 cases), tricuspid severe reflux and pulmonary hypertension (1 case), hydrocephaly (5 cases), muscular dystonia (three cases with hypertonia, and four with hypotonia), convulsion (7 cases), apnea, sobbing respiration (10 cases), chromatosis (6 cases), anemia (13 cases), edema (6 cases), thrombocytopenia (6 cases), hematuria and proteinuria (2 cases). Five cases gave up therapy before diagnosis was made. Sixteen cases received the treatment with Vitamin B12 and supplementation of L-carnitine. Seven cases gave up after treatment without effect or deterioration of condition. Eight cases were vitamin B12-responsive, and one case was vitamin B12-nonresponsive. The follow-up for a period ranging from three months to two years, among eight vitamin B12responsive cases, 6 cases showed a favorable outcome with apparent improvement, one case had no symptom and one patient died from severe pneumonia. Vitamin B12-nonresponsive case was still alive. Conclusions　The clinical manifestations of MMA are non-specific. Urine organic acid analysis is critical to early diagnosis of MMA in high-risk patients. Timely diagnosis and appropriate long-term treatment are essential to improve the prognosis of the disease.