Background : Gut microbiota may play a role in the severity of atopic dermatitis Objective : We sought to examine the association between early life gut microbiota and the severity of atopic dermatitis(AD). Methods : Fecal samples were collected at age 6 months and 161 infants were followed with AD diagnosis by a pediatric allergist at 6, 12 months and severity of AD symptoms assessed by the SCORAD (Scoring Atopic Dermatitis) index. The composition of gut microbiota was analyzed in fecal samples from 161 infants by pyrosequencing, including 88 healthy infants, 27 infants with mild AD, and 46 infants with moderate to severe AD. Results : Gut microbiome composition at age 6 months was associated with enrichment of Streptococcus and reduction of Clostrdium g6 in gut microbiome of subjects with moderate to severe AD. The relative abundance of Streptococcus was positive correlated with SCORAD index and serum IgE levels in AD group. The relative abundance of Clostridium g6 was negative correlated with SCORAD index and eosinophils(%) in AD group. Among the infants with AD at 6 months, Streptococcus was abundant in 6 month gut microbiome in persistency e AD group when divided into persistent AD group and improved group up to 1 year old. Conclusions : Early-life gut microbiome may be associated with severity of AD and shape AD outcomes in childhood. This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number : HI14C2687) and a fund (2014-ER5602-00) by Research of Korea Centers for Disease Control and Prevention.