Anticancer effect of methanol extract of Caesalpinia sappan L. on oral carcinoma(KB) and osteosarcoma(HOS) cells were investigated in this study. In order to elucidate the anticancer mechanism of Caesalpinia sappan L, we analyzed telomerase inhibitory effect of the methanol extract of Caesalpinia sappan L. In addition, we prepared 5 fraction samples according to its polarity differences and analyzed anticancer effects on oral carcinoma and osteosarcoma cells. Following results are obtained in this study. 1. 50% cell proliferation inhibitory value($IC_{50}$) of the methanol extract of Caesalpinia sappan L. against oral carcinoma(KB) cells and osteosarco ma(HOS) cells were $9.0{mu}g/ml;and;10.9{mu}g/ml$, respectively. 2. The methanol extract of Caesalpinia sappan L. showed inhibitory effect of telomerase which is required for cancer cell immortality. Therefore, it seems that the anticancer effect of methanol extract of Caesalpinia sappan is at least partially due to telomerase inhibitory effect. 3. Five fraction samples were prepared according to its polarity and 88.7% of ingredient of total methanol extract was transferred to ethylacetate fraction. Thin layer chromatography analysis showed that dichloromethane fraction contained ingredient with relatively high polarity and ethylacetate fraction contained similar ingredient found in total methanol extract. 4. Anticancer effect was observed in n-hexane, dichloromethane, and ethylacetate fractions. The highest anticancer effect was found in dichloromethane fraction which had $IC_{50}$ value of $4.4{mu}g/ml$ and > $4.0{mu}g/ml$ against oral carcinoma(KB) cells and osteosarcoma(HOS) cells, respectively.