ABSTRACT: Analyze the pathogen composition of late-onset bacterial sepsis in very and extremely low birth weight, study the characteristics of late-onset sepsis caused by G-bacteria and G+ bacteria.Methods Totally 62 very and extremely birth weight infants during April 2012 to March 2018 were analyzed. According to the results of blood culture, they were divided into two groups：gram-negative bacteria and gram-positive bacterial infection group. The maternal pregnancy,clinical feature and laboratory results of the two groups were compared.Results The incidence of late-onset bacterial sepsis in very and extremely low birth weight infants was 10.53%（62/589）. Gram-positive pathogens accounted for 71.9%, mainly Staphylococcus epidermidis (37.0%). Gram-negative pathogens accounted for 28.1%, Enterobacter cloacae and Klebsiella pneumoniae ranked first，all accounted for 33.3%. Compared with gram-positive pathogens group, the leukocyte decline, abdominal distention and thrombocytopenia in gram-negative bacteria group were increasing significantly (P<0.05). Compared with gram-positive pathogens group, the mortality rate or abandonment of gram-negative bacteria group was increasing significantly(P<0.05).Conclusions Gram-positive pathogens are the main pathogens causing septicemia in very and extremely low birth weight infants. Gram-negative pathogens infection is more likely to develop abdominal distention. Laboratory tests showed leukocyte reduction and thrombocytopenia. Early selection of antibiotics based on clinical feature and laboratory results may improve the rationality of clinical medication.