The effect of methanol soluble fraction(MSF) of kimchi on the proliferating and differentiating activity of normal rat mammary epithelial cells or organoids in culture were studied. Reconstituted basement membrane, Matrigel, supported the growth and development several different multicellular structures from mammary organoids. The five type colonies of multicellular structures, stellate, ductal, webbed, squamous, and lobulo-ductal colonies, were observed in Matrigel culture. In methanol extract groups, webbed colonies were more and squamous colonies were less than control group. and the lobulo-ductal colonies which is known that it formed in well differentiated mammary epoithelial cells were developed more in MSF treated group than control group. These results showed that methanol extract of kimchi affected on the proliferation and differentiation of normal rat mammary epithelial cells cultured in serum free medium condition.