Atopic dermatitis (AD) is a chronic inflammatory skin disease, with a complex etiology encompassing immunologic responses. AD is frequently associated with elevated serum immunoglobulin (Ig) E levels and is exacerbated by a variety of environmental factors, which contribute to its pathogenesis. However, the etiology of AD remains unknown. Recently, reports have documented the role of lactic acid bacteria (LAB) in the treatment and prevention of AD in humans and mice. The LAB, Lactobacillus casei (LC), is frequently used in the treatment of AD. To identify the active component of LC, we screened fractions obtained from the ion exchange chromatography of LC extracts. Using this approach, we identified the candidate protein, P14. We examined whether the P14 protein has anti-atopic properties, using both in vitro and in vivo models. Our results showed that the P14 protein selectively downregulated serum IgE and interleukin-4 cytokine levels, as well as the AD index and scratching score in AD-like NC/Nga mice. In addition, histological examination was also effective in mice. These results suggest that the P14 protein has potential therapeutic effects and that it may also serve as an effective immunomodulatory agent for treating patients with AD.