Objective To investigate the value of tandem mass spectrometry( MS / MS) in the etiological diagnosis of cholestasis in infants.Methods A total of 153 infants with cholestasis who visited the Department of Pediatrics,Shengjing Hospital,China Medical University,from January 2013 to March 2015 were studied. All of them underwent blood and urine examinations by MS / MS. The patients' medical history and physical examination characteristics were recorded. Clinical examination results in biochemistry,etiology,and imageology were analyzed. Blood test and urine test were carried out by high- performance liquid chromatography- tandem mass spectrometry( HPLC- MS /MS) and gas chromatography- mass spectrometry( GC- MS),respectively. For the patients with abnormal blood or urine MS / MS results,potential pathogenic genes were determined. Comparison of continuous data was made by non- parametric Mann- Whitney U test and comparison of categorical data was made by chi- square test. Results Among the 153 infants with cholestasis,19( 12. 4%) had abnormal blood or urine MS / MS results. According to clinical data and gene analysis,15 infants among them were diagnosed with neonatal intrahepatic cholestasis caused by citrin deficiency,2 infants with tyrosinemia,1 infant with methioninemia,and another 1 infant with propionic acidemia. Compared with the normal MS / MS group of infants,the abnormal MS / MS group had significantly longer jaundice duration( Z =-2. 227,P < 0. 05) and significantly higher levels of alkaline phosphatase,gamma- glutamyl transferase,and total bile acids( 830. 0 vs523. 0 U / L,Z =- 3. 185,P < 0. 05; 215. 0 vs 160. 0 U / L,Z =- 2. 130,P < 0. 05; 174. 8 vs 125. 7 μmol / L,Z =- 2. 351,P < 0. 05). Significant differences were also found in prothrombin time and activated partial thromboplastin time( Z =- 4. 300,P < 0. 001; Z =- 3. 526,P <0. 001).Cytomegalovirus was detected in 58. 8%( 90 /153) of all patients and in 78. 9%( 15 /19) of patients with abnormal MS / MS results. Conclusions Given the non- specificity of clinical manifestations and biochemical examinations for infantile cholestasis of different causes,MS / MS can be used as the first choice of early screening method and plays an important role in the etiological diagnosis of cholestasis in infants,especially in the identification of cholestasis caused by genetic and metabolic disorders.