Zinc deficiency in patients with atopic dermatitis (AD) and the use of zinc supplementation is still controversial. We measured hair zinc levels in 58 children with AD and 43 controls (age range 2-14 years). We also investigated the efficacy of oral zinc supplementation in AD patients with low hair zinc levels by comparing eczema assessment severity index (EASI), transepidermal water loss (TEWL), and visual analogue scales for pruritus and sleep disturbance in patients receiving zinc supplementation (Group A) and others not receiving supplementation (Group B). At baseline, the mean zinc level was significantly reduced in AD patients (113.1 μg/g vs. 130.9 μg/g, p = 0.012). After 8 weeks of supplement, hair zinc level increased significantly in Group A (p < 0.001), and EASI scores, TEWL, and visual analogue scales for pruritus improved more in Group A than in Group B (p = 0.044, 0.015 and < 0.001, respectively). Thus, oral zinc supplementation may be effective in AD patients with low hair zinc levels.