Purpose: This study was conducted to investigate the anti-proliferative effects of Ulmi Pumilae Cortex Extracts(UPCE) on MCF-7(human, breast, adenocaecinoma) and NIH3T3 (human, murine, fibroblast). Methods: MCF-7 cells and NIH3T3 cells were cultured and seeded in cell culture plates, respectively. UPC was extracted with hot water and then further fractionated it into five types: hexane, chloroform, ethyl acetate, butanol, and water soluable fractions. These five different fractions from UPCE were tested for their anti-proliferative effects on MCF-7 cells and NIH3T3 cells by MMT assay. Results: Among the five solvent-fractions of UPCE, n-hexane fraction and ethyl acetate fraction showed a strong anti-proliferative effects on MCF-7 cells but they displayed significant cytotoxicity on NIH3T3 cells, too. On the other hand, chloroform fraction showed a marked anti-proliferative effects on MCF-7 cells and low cytotoxicity on NIH3T3 cells. Conclusion: Chloloform fraction from UPCE showed selective anti-cancer activities on human breast cancer cell MCF-7 relatively to the other fractions.