Background B7 homolog 3 (B7-H3), a member of the immunoregulatory ligand B7 family, is pivotal in T-cell-mediated immune response. It is widely expressed in diverse human tumors and its high expression indicates the poor prognosis of the patients. Nonetheless, B7-H3's role in colorectal cancer (CRC) needs to be further explored. Methods Western blot and immunohistochemistry were employed for detecting B7-H3 protein expression in CRC tissues and cell lines, respectively. Quantitative real-time polymerase chain reaction (qRT-PCR) was utilized for detecting B7-H3 mRNA and miR-128 expression levels. CRC cell lines SW620 and HT29 were used to construct B7-H3 overexpression or knockdown cell models, respectively. Cell counting kit-8 (CCK-8), 5-bromo-2 '-deoxyuridine (BrdU), and scratch wound healing assays were employed for evaluating the effects of B7-H3 on CRC cell multiplication and migration. Besides, the regulatory relationship between miR-128 and B7-H3 was validated through dual-luciferase reporter gene assay, qRT-PCR, and western blotting. Results B7-H3 expression level was remarkably elevated in CRC tissues and cell lines, and its high expression level was associated with increased tumor size, positive lymph node metastasis, and increased T stage. In CRC cells, B7-H3 overexpression significantly facilitated the cell multiplication and migration, while B7-H3 knockdown worked oppositely. Moreover, B7-H3 was identified as a target of miR-128, and miR-128 negatively regulated B7-H3 expression in CRC cells. Conclusion B7-H3 expression is upregulated in CRC tissues and cell lines, and B7-H3 participates in promoting the proliferation and migration of CRC cells. Besides, B7-H3 expression is negatively regulated by miR-128 in CRC.