Objective To evaluate the relationship between the severity of neonatal infection and the activity change of cardiac enzyme. Methods A total of 102 infectious neonates in NICU were evaluated with neonatal serious illness scoring system and then divided into non-critical, critical, and extremely-critical groups. The activity of such serum myocardial enzymes as AST, ALT, LDH, CK, and CKMB was tested in the first 24 hours on admission. Comparison between groups and analyses were conducted. Resultes Myocardial enzyme of the critical and extremely-critical groups was obviously higher than that of the non-critical group (Plt;0.01). Conclusion The serious illness score of infectious neonates is closely associated with the activity change of myocardial enzyme and the level of serum myocardial enzymes has certain advantages in judging the myocardial injury and the disease severity of neonatal infection.