In vitro cytotoxicity and antioxidative effects of water extracts prepared from Mustard Leaf Kimchi (MLK) during its fermentation period were investigated. The cytotoxicity against HepG2 (human hepatic cancer) by water extracts from the well fermented Mustard Leaf Kimchi was higher than others (fermented for 0 to 6 days at 18$^{circ}C$), and IC50 of water extracts at the points of 6, 8, 10, and 14days during fermentation were 213.4, 99.2, 99.9, and 109.8${mu}{ extrm}{m}$/ml, respectively. Antioxidative activity of water extracts from MLK during various fermentation periods was higher than that of blank distilled water. However, the antioxidative activity of well-fermented water extracts of MLK (fermented for 8-14 days) did not show any difference from that of others (fermented for 2-6 days). Thus, water extracts of well-fermented MLK (fermented during 8-14 days) significantly inhibited the growth of cancer cells in vitro, but little antioxidative activity was influenced by the various fermentation periods.