Background: Diet-gut microbiota-disease hypothesis for atopic dermatitis (AD) has been studied in infancy, but its implications for preschool-aged children remain less understood. This study aims to investigate the relationships among dietary patterns, gut microbiota, and disease severity in Korean preschoolers. Methods: We evaluated 97 preschool children aged 3–6 years, including 46 with AD and 51 healthy controls (CON). Dietary intake was assessed using a Food Frequency Questionnaire (FFQ), and dietary patterns were analyzed through factor analysis of the FFQ. AD severity was assessed using EASI, SCORAD and CDLQI scores. Gut microbiota composition was characterized using 16S rRNA sequencing. Results: Through factor analysis of food group, Q1 (Traditional Korean Diet Pattern) and Q2 (Processed Food and Snack Pattern) were identified. AD-Q2 diet had lower vitamin C intake compared to those on the AD-Q1 diet (p=0.011). Dorea and Anaerostipes were more prevalent in the AD-Q2 group (LDA score: 3.4 and 3.9, respectively). The AD-Q2 group also reported significantly poor CDLQI and high nighttime itching compared to the AD-Q1 group (p=0.032 and 0.041, respectively). Insufficient intake of vitamin C was significantly associated with increased EASI and SCORAD (r = -0.52, p = 0.03; r = -0.41, p = 0.045, respectively), whereas the presence of Dorea and Anaerostipes also positively correlated with itching. Conclusions: In preschool children with AD, the Processed Food and Snack dietary pattern was associated with increased disease severity, potentially mediated by Dorea and Anaerostipes abundance and vitamin C deficiency, impacting the gut environment and inflammation pathways.