The prevalence of atopic dermatitis (AD) in school-age children has increased in industrialized countries. As diet is one of the main factors provoking AD, some studies have suggested that food additives in processed foods could function as pseudoallergens, which comprise the non-immunoglobulin E-mediated reaction. Eosinophil cationic protein (ECP) is an eosinophil granule protein released during allergic reactions to food allergens in patients with AD. Thus, serum ECP levels may be a useful indicator of ongoing inflammatory processes in patients with AD. The purpose of this study was to investigate the effect of consuming MSG in processed foods on serum ECP levels among children with AD. This study was performed with 13 patients with AD (age, 7-11 years) who had a normal range of total IgE levels (< 300 IU/ml). All participants ate normal diets during the first week. Then, six patients were allocated to a processed food-restricted group (PRDG) and seven patients were in a general diet group (GDG). During the second week, children in the PRDG and their parents were asked to avoid eating all processed foods. On the third week, children in the PRDG were allowed all foods, as were the children in the GDG throughout the 3-week period. The subjects were asked to complete a dietary record during the trial period. Children with AD who received the dietary restriction showed decreased consumption of MSG and decreased serum ECP levels and an improved SCORing score on the atopic dermatitis index (P < 0.05). No differences in serum ECP levels or MSG consumption were observed in the GDG. Serum total IgE levels were not changed in either group. In conclusion, a reduction in MSG intake by restricting processed food consumption may lead to a decrease in serum ECP levels in children with AD and improve AD symptoms.