Colorectal cancer is one of the most malignant neoplasms worldwide. Fucoxanthin is a carotenoid present in the chloroplasts of brown seaweeds. In the present study, the anticancer effects of fucoxanthin and its metabolite, fucoxanthinol, on 6 colorectal cancer cell lines and 20 tissue samples from surgically resected clinical colorectal cancer specimens were examined using a collagen-gel droplet embedded culture drug sensitivity test (CD-DST). The in vitro sensitivity to fucoxanthin, fucoxanthinol and the anticancer drugs is expressed as T/C (%), where T is the absorbance of cells which stained by neutral red treated with carotenoids and C is the absorbance of non-staining cells. Fucoxanthin and fucoxanthinol decreased the T/C (%) of Caco-2, WiDr, HCT116, and DLD-1 cell lines at doses of 20 µM. Fucoxanthinol also decreased the T/C (%) of SW620 cells, while the T/C (%) of Colo205 cells was not reduced by treatment with either carotenoid. Specifically, the T/C (%) of Caco-2 and WiDr cells, which were incubated in carotenoid-free medium for 6 days following treatment with 20 µM fucoxanthinol for 24 h, was markedly decreased to 1.4±0.2 and 12.0±0.3%, respectively. Furthermore, fucoxanthin and fucoxanthinol decreased the T/C (%) in colorectal cancer tissue samples. Notably, 20 µM fucoxanthinol treatment resulted in a higher proportion of colorectal cancer samples with a T/C (%) of <50% (13/20, 65%) compared with samples treated with 20 µM fucoxanthin (2/20, 10%). The median T/C (%) value of 35.1% for the 20 cancers specimens treated with 20 µM fucoxanthinol was lower than the median T/C (%) values of 86.3% and 75.8% for those treated with fluorouracil and paclitaxel, respectively. These results suggested that fucoxanthin and fucoxanthinol may be of use as chemotherapeutic agents in colorectal cancer.