Background: Atopic dermatitis (AD) is chronic pruritic inflammatory skin disease in children. Interleukin (IL) 31 is a recently discovered cytokine associated with chronic skin inflammation and pruritus. Objectives: The aims of this study were to determine whether serum IL-31 levels are increased in children with AD and to examine the relationship between IL-31 and other clinical biomarkers in AD. Methods: Serum cytokine levels, including IL-31, IL-4, and IL-12, were measured in 38 patients with AD and 10 healthy children. Peripheral blood eosinophils, serum immunoglobulin E levels, eosinophil cationic protein, and thymic stromal lymphopoietin (TSLP) were measured. We also estimated the clinical severity of AD by using the Scoring Atopic Dermatitis (SCORAD) index by a single clinician. Results: The serum IL-31 levels were significantly higher in the patients with AD than in the healthy children. IL-31 correlated well with the SCORAD index and blood eosinophilic inflammatory markers. The serum level of TSLP was also higher in patients with AD than in the healthy children; however, levels of IL-4 and IL-12 were not different between AD and healthy children. There was no significant difference in serum IL-31 levels between patients with atopic AD and nonatopic AD. Conclusion: This study showed that serum IL-31 levels were significantly elevated in patients with AD than in the healthy children and correlated well with disease severity. IL-31 seemed to be one of the cytokines that induce pruritus and eosinophilic inflammation in AD. Serum IL-31 correlated with pruritic symptoms and disease course of AD.