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The cytochrome P450 monooxygenases (CYP450) are the largest enzyme family in plant metabolism and widely involved in the biosynthesis of primary and secondary metabolites. Foxtail millet (<i>Setaria italica</i> (L.) P. <i>Beauv</i>) can respond to abiotic stress through a highly complex polygene regulatory network, in which the SiCYP450 family is also involved. Although the CYP450 superfamily has been systematically studied in a few species, the research on the CYP450 superfamily in foxtail millet has not been completed. In this study, three hundred and thirty-one <i>SiCYP450</i> genes were identified in the foxtail millet genome by bioinformatics methods, which were divided into four groups, including forty-six subgroups. One hundred and sixteen genes were distributed in thirty-three tandem duplicated gene clusters. Chromosome mapping showed that SiCYP450 was distributed on seven chromosomes. In the SiCYP450 family of foxtail millet, 20 conserved motifs were identified. <i>Cis</i>-acting elements in the promoter region of <i>SiCYP450</i> genes showed that hormone response elements were found in all <i>SiCYP450</i> genes. Of the three hundred and thirty-one <i>SiCYP450</i> genes, nine genes were colinear with the <i>Arabidopsis thaliana</i> genes. Two hundred <i>SiCYP450</i> genes were colinear with the <i>Setaria viridis</i> genes, including two hundred and forty-five gene duplication events. The expression profiles of <i>SiCYP450</i> genes in different organs and developmental stages showed that <i>SiCYP450</i> was preferentially expressed in specific tissues, and many tissue-specific genes were identified, such as <i>SiCYP75B6</i>, <i>SiCYP96A7</i>, <i>SiCYP71A55</i>, <i>SiCYP71A61</i>, and <i>SiCYP71A62</i> in the root, <i>SiCYP78A1</i> and <i>SiCYP94D9</i> in leaves, and <i>SiCYP78A6</i> in the ear. The RT-PCR data showed that <i>SiCYP450</i> could respond to abiotic stresses, ABA, and herbicides in foxtail millet. Among them, the expression levels of <i>SiCYP709B4</i>, <i>SiCYP71A11</i>, <i>SiCYP71A14</i>, <i>SiCYP78A1</i>, <i>SiCYP94C3</i>, and <i>SiCYP94C4</i> were significantly increased under the treatment of mesotrione, florasulam, nicosulfuron, fluroxypyr, and sethoxydim, indicating that the same gene might respond to multiple herbicides. The results of this study will help reveal the biological functions of the SiCYP450 family in development regulation and stress response and provide a basis for molecular breeding of foxtail millet.