Interleukin (IL)-8 (CXCL8) expression has been found to be increased in mast cells in atopic dermatitis. It is the most important chemoattractant for immune cells. Pyeongwee-San is a traditional Korean medicine which has been using as a useful prescription for treatment of atopic dermatitis. The objective of this study was to determine precisely the effect of Pyeongwee-San extract (KMP6) on IL-8 expression using human mast cell line, HMC-1 cells. KMP6, HS-Pyeongwee-San (HS-PS, an over-the-counter drug of the Han Kook Shin Yak Pharmaceutical Co., LTD.), and the important component of KMP6, hesperidin inhibited the phorbol 12-myristate 13-acetate and calcium ionophore A23187-induced IL-8 secretion and mRNA expression in HMC-1 cells. These effects were better than those of dexamethasone, the reference drug tested in our experimental model. Our results revealed the effect of KMP6, which may act as a promising therapeutic agent for the treatment of atopic dermatitis.