Although astragaloside IV exhibits anti-inflammation, immunoregulatory, and anticancer properties, the chemosensitization effects of astragaloside IV in colorectal cancer have never been reported. Our study tested whether astragaloside could increase cisplatin sensitivity in colorectal cancer. CCK-8 assay was used to measure the cell viability of colorectal cancer cells. Quantitative real-time PCR and Western blot were performed to determine the mRNA and protein expression, respectively. Our data revealed that astragaloside IV administration significantly suppressed the cell growth of colorectal cancer cells, whereas no obvious cytotoxicity of astragaloside IV was observed in nonmalignant colonic cells. In addition, combined treatment with astragaloside IV dramatically elevated the chemosensitivity of colorectal cancer cells to cisplatin. Mechanical investigation revealed that the mRNA and protein expression of NOTCH3 was significantly lower in cisplatin and astragaloside IV-treated cells compared with cells treated with cisplatin alone. On the contrary, no obvious changes in tumor cell growth were shown after upregulation of NOTCH3 whether in the presence or absence of astragaloside IV. Thus, our data demonstrate that astragaloside IV increases the chemosensitivity of colorectal cancer cells to cisplatin, at least partly, through inhibition of NOTCH3. This study suggests that combined therapy with astragaloside IV might be a novel therapeutic approach for colorectal cancer.