Background/Aim: Fucoxanthinol (FxOH), a marine carotenoid, induces apoptosis and anoikis in human colorectal cancer (CRC) DLD-1 cells via the down-regulation of chloride intracellular channel 4 (CLIC4) expression, a key molecule for apoptosis. However, whether FxOH is susceptible to CLIC4 expression and its regulatory mechanisms in human CRC cells remains unknown. We investigated the inhibitory effects of FxOH on six types of human CRC cells with CLIC4 regulation. Materials and Methods: The association between FxOH and CLIC4 was investigated using gene knockdown, overexpression, and transcriptome analyses. Results: CLIC4 expression in CRC cells was a significant factor associated with sensitivity to FxOH. CLIC4 regulates many cancer-related signals and participates in growth inhibition in FxOH-treated DLD-1 cells. Both CLIC4 knockdown and overexpression attenuated the inhibitory effects of FxOH on DLD-1 cells. Conclusion: Our findings suggest that the protein expression of CLIC4 and its regulating mechanisms play significant roles regarding cell death in human CRC cells by FxOH treatment. Further investigation by in vitro and in vivo models is needed to determine the effect of CLIC4.Colorectal cancer (CRC) is one of most prevalent cancers, with the third highest number of new cases (1.9 million per a total of 19.3 million) and second highest number of new deaths (0.9 million per a total of 10.0 million) worldwide, as estimated using the Global Cancer Observatory: CANCER TODAY 2020 database (1). The global incidence and mortality rates of CRC are expected to increase to more than 2.2 million new cases and 1.1 million deaths, respectively, by 2030 (2).Point mutations in certain driver genes, such as adenomatous polyposis coli, Kirsten-ras (KRAS) and tumor protein p53 (Tp53), and aberrant regulations of many other genes and processes, such as signal transduction, tumor microenvironment formation, immune suppression, and gut microbiota alteration, are considered to contribute to carcinogenesis and disease progression (3-14).The chloride intracellular channel (CLIC) protein family is a group of small globular proteins (28 kDa) comprising seven members: CLIC1, CLIC2, CLIC3, CLIC4, CLIC5A, CLIC5B, and CLIC6. They are ubiquitously expressed in various tissues and involved in intracellular trafficking, membrane remodeling, and other homeostatic mechanisms (15). Among these, CLIC4 has been well-studied for its association with cancer development. CLIC4 is a key molecule for apoptosis, angiogenesis, cell adhesion, wound healing, and tumorigenesis (14-20). In addition, CLIC4 expression is regulated by KRAS and Tp53 (21,22). We recently revealed that the number of CLIC4 high-expressing cells tended to decrease with the progression of pathological grades in colorectal malignant tissues of patients with CRC (23). These findings were also consistent with those of a previous study (24). Moreover, high expression levels of CLIC4 protein are suggested to be correlated with poor prognosis in patients with CRC and the aggressive pote...