Aims Atopic dermatitis (AD) is a chronic inflammatory skin disease, with a steadily increasing prevalence. Lactic acid bacteria (LAB) have been widely used in the food industry and are an attractive option for preventing and treating allergic skin diseases. We previously isolated new LABs including Lactococcus lactis KR-050L from Gajuknamu kimchi, and showed the anti-inflammatory effects of extract of L. lactis KR-050L culture broth (LLK). In this study, we investigated the effects of LLK on AD. Methods and Results For the in vitro study, we used human keratinocytes (HaCaT) and mast cells (RBL-2H3). In vivo study, we investigated the effects of LLK on Dermatophagoides farinae extract (DFE) and 2,4-dinitrochlorobenzene (DNCB)-induced atopic skin inflammation in mice. LLK suppressed expression of pro-inflammatory cytokines and chemokines by down-regulation of p38 MAPK, STAT1 and nuclear translocation of NF-kappa B in keratinocytes. Topical application of LLK suppressed AD symptoms based on reduction in ear thickness, serum IgE levels and immune cell infiltration. Furthermore, LLK inhibited serum histamine levels and mast cells infiltration in vivo, and reduced mast cells activation in vitro. Conclusions These results suggest that LLK inhibits AD symptoms through inhibition of keratinocytes and mast cells activation. Significance and Impact of the Study LLK is a potential therapeutic candidate for AD treatment.