Cornus kousa Burg. (Cornaceae) is a small deciduous tree characterized by brilliant, colorful, and attractive flowers and fruits. It is widely distributed in the northern hemisphere, such as eastern Asia and eastern and northern parts of the United States. C. kousa is widely cultivated for ornamental purposes in eastern Asia. The fruits of this plant have been used as a hemostatic agent and for the treatment of diarrhea in Korean traditional medicine [1]. Additionally, immuno-regulatory properties for this fruit extract have been reported [2]. Some chemical constituents such as isoquercitrin, gallic acid, tannin, phenolics, and flavonoids [3] have been reported to be present in the leaves of C. kousa. Also, our previous phytochemical research on the fruits of this plant demonstrated the presence of steroids [4], cytotoxic lignans [5], and flavonoids [6]. Bioactivity-guided fractionation led to the isolation of cytotoxic triterpenoids from the fruits of C. kousa. When the methanol extracts of C. kousa were developed on silica gel TLC, pink and purple spots appeared after spraying with 10% H2SO4 solution and heating, indicating the presence of triterpenoids in the extracts. The methanol extract was fractionated into an EtOAc layer, an n-BuOH layer, and a H2O layer through solvent fractionation. The repeated silica gel (SiO2), octadecyl silica gel (ODS), and Sephadex LH-20 column chromatographies (c.c.) of EtOAc fractions yielded ten triterpenoids, compounds 1–10. The chemical structures of the triterpenoids were determined from spectroscopic analysis, including EI/FAB-MS, IR, PMR, 13C NMR, DEPT, and 2D NMR (COSY, HSQC, HMBC). The compounds were revealed to be ursolic acid (1) [7], lupeol (2) [8], taraxasterol (3) [9], betulinic acid (4) [10], betulinic aldehyde (5) [11], ursolic aldehyde (6) [7], arjunolic acid (7) [12], tormentic acid (8) [13], asiatic acid (9) [14], and 19 -hydroxyasiatic acid (10) [15]. Although these compounds were previously isolated from other plants, this is the first report of their isolation from C. kousa. All isolated compounds were evaluated for their cytotoxicity against human colon carcinoma (HCT-116), human breast carcinoma (MCF-7), human cervix carcinoma (HeLa), human ovary carcinoma (SK-OV-3), and human melanoma (SK-MEL-5) using the MTT assay. As shown in Table 2, some compounds inhibited the growth of human cancer cell lines. In conclusion, the findings of this study suggest that the methanolic extract of C. kousa, as well as its isolated triterpenoids, may prove useful for the treatment of human cancer. Plant Materials. The fruits of Cornus kousa Burg. (Cornaceae) were collected at the experimental farm at Kyung Hee University in August 2006 and identified by Prof. Dae-Keun Kim, College of Pharmacy, Woosuk University, Jeonju, Korea. A voucher specimen (KHU060907) was reserved at the Laboratory of Natural Products Chemistry, Kyung Hee University, Yongin, Korea.