Atopic dermatitis is caused by various factors, including complex interactions between immune responses and imbalances in T helper cells. In order to resolve the side effects of steroid-based treatment and rapidly improve atopy symptoms, the development of preventive substances for new treatments and as food supplements is essential. Nakai (PKN) is traditionally used as an effective herbal medicine for pain relief, anti-inflammation, and edema, and dried PKN is boiled and drunk as a tea to prevent them; however, its effect on skin manifestations such as atopy are unclear. Therefore, we investigated the in vivo and in vitro effects of PKN extract on improving symptoms of atopy as a potential treatment. By evaluating dermatitis scores and conducting histopathological analysis in mice with Dermatophagoides farina-induced atopy-like pathology, we demonstrated that PKN extract alleviated atopy symptoms. Moreover, PKN extract restored a reduction in the protein levels of skin barrier-related factors in skin tissue. Through in vitro analysis, we examined the impact of PKN on JAK/STAT signaling in IL-4/IL-13-stimulated human keratinocytes and elucidated the mechanisms that suppress the levels of skin barrier factors and inflammation. PKN extract inhibited JAK/STAT phosphorylation stimulated by IL-4/IL-13. Furthermore, docking analysis of PKN constituents indicated binding to JNK1/2 and STAT3/6 and a subsequent inhibition of signal transduction. Therefore, this suggests that PKN extract has potential not only as a treatment but also as a food supplement to improve atopic dermatitis by strengthening skin barrier factors and inhibiting key signaling molecules.