By a series of in vitro and in vivo functional studies, we demonstrated that CYP2S1 knockdown selectively inhibited cell proliferation, colony formation, migration, invasion, and tumorigenic potential in nude mice, and induced cell apoptosis in BRAFV600E-mutated thyroid cancer cells, but not in BRAF wild-type ones. This evidence concerns the gene CYP2S1 and thyroid cancer.