The purpose of this research was to study the effects of kefir whey (kefir whey, peptides, lactic acid) on skin care properties including skin lightening effect and acne treatment. The final aim was to develop a new cosmetic product and enhance the value of dairy products. The results of skin lightening tests showed that all three kefir whey components (kefir whey, peptides and lactic acid) had inhibitory ability against melanin synthesis. Furthermore, copper chelating analysis demonstrated that both kefir whey and kefir whey peptides could chelate the copper in tyrosinase, which might explain the mechanism of inhibition. The ability for acne treatment indicated that lactic acid level higher than 60 mg/ml could inhibit the growth of Propionibacterium acne, whereas no inhibition was found with other components.