Cryptotaenia canadensis subsp. Japonica, which is called mitsuba in Japan, is an herbal plant indigenous to Asia that grows in the shade in the mountains. Mitsuba has been cultivated since the Edo period, and has been used in Japan as a traditional medicine and spice. It is believed that this plant contains active constituents that induce various effects, such as appetite stimulation and sedation. A recent report, moreover, has revealed that the methanol extract of dried mitsuba has remarkable anti-inflammatory effects against macrophage cells, although other activities remain to be elucidated. In this study, we investigated whether the extract from mitsuba leaves (MTBE) has anti-oxidative effects in RAW264.7 mouse macrophage-like cells. MTBE was prepared by chloroform extraction, and cell viability was determined with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. MTBE did not have anti-oxidative effects but instead induced cell death at high concentrations. To elucidate the mechanisms underlying MTBE-induced cell death, the effects of antioxidants (N-acetyl cysteine and catalase) and a Ca2+ chelator (membrane permeable BAPTA) were examined. However, cell death was not suppressed by these reagents. Furthermore, we explored whether MTBE induced apoptosis and found that caspase-3 was activated. Taken together, these results suggested that high concentrations of MTBE induced apoptosis. We are now trying to clarify the MTBE constituents that induce apoptosis.