Buckwheat (Fagopyrum esculentum Moench) hull was extracted with 70% ethanol and then further fractionated with n-hexane, chloroform, ethyl acetate, and water stepwise. In the in vitro test (SRB assay), hexane and ethyl acetate fractions showed higher inhibition effects against MCF-7 cells than other samples at the 1 mg/mL level: 89% and 93.2%, respectively. They also displayed higher inhibition rates against Hep3B cells of 83.6% and 75.3%, respectively, at 1 mg/mL. The ethyl acetate fraction yielded the highest inhibition rate against A549 cells with the level of 0.25 mg/mL, but it showed a lower inhibition rate than the hexane and chloroform fractions at higher levels of sample, i.e., 0.75 and 1.0 mg/mL. All samples showed higher inhibition effects against AGS human gastric carcinoma than any other cancer cells. The inhibition rates against HeLa cells were 81.2% and 82.0% for the chloroform and butanol fraction with 0.5 mg/mL, respectively. However, all samples yielded an inhibition rate of less than 35% against normal cells, at all treatment levels, except the ethanol extract. All extracts at doses of 25 and 50 mg/kg showed decreases of more than 20% and 42%, respectively, in tumor formation in sarcoma-180 implanted mice except for the aqueous fraction. From these results, it is suggested that buckwheat hull possesses anticancer properties against a variety of different cancer cell lines.