This study was carried out to evaluate cytotoxic effects of Houttuynia cordata Thunberg extracts on murine leukemia tumor cell lines. Disruptions in cell organelles were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazol iumbromide (MMT) assay. The comparison of $IC_{50}$ values of Houttuynia cordata Thunberg extracts on $L1210,;P388D_1$ and Vero cell lines showed that the methanol extract of Houttuynia cordata Thunberg indicated the most antitumor activity in the MTT assay. In order to develop a antimicrobial agent, dried Houttuynia cordata Thunberg was extracted with several solvents, and then antimicrobial activity was investigated. The minimal inhibitory concentration (MIC) of the extracted substance against microorganisms were also examined. Antimicrobial activity of amocla and ketoconazole as references was compared to those of other solvent extracts such as $H_2O$, n-hexane, chloroform, ethyl acetate ethanol and methanol. The antimicrobial activity of all extracts from the sample had growth inhibition activity against gram-negative bacteria, yam-positive bacteria and fungi $(MIC,;>;200;{mu} g/ml)$. These results suggest that the methanol soluble extract of Houttuynia cordata Thunberg may be a valuable choice for the studies on the treaeent of murine leukemia tumor cell lines and antimicrobial agents.