Background Cannabis, an important industrial crop, has a high sensitivity to photoperiods. The flowering time of cannabis is one of its important agronomic traits, and has a significant effect on its yield and quality. The CONSTANS-like (COL) gene plays a key role in the regulation of flowering in this plant. However, the specific roles of the COL gene family in cannabis are still unknown. Results In this study, 13 CsCOL genes were identified in the cannabis genome. Phylogenetic analysis implied that the CsCOL proteins were divided into three subgroups, and each subgroup included conserved intron/exon structures and motifs. Chromosome distribution analysis showed that 13 CsCOL genes were unevenly distributed on 7 chromosomes, with chromosome 10 having the most CsCOL members. Collinearity analysis showed that two syntenic gene pairs of CsCOL4 and CsCOL11 were found in both rice and Gossypium raimondii. Of the 13 CsCOL genes, CsCOL6 and CsCOL12 were a pair of tandem duplicated genes, whereas CsCOL8 and CsCOL11 may have resulted from segmental duplication. Furthermore, tissue-specific expression showed that 10 CsCOL genes were preferentially expressed in the leaves, 1 CsCOL in the stem, and 2 CsCOL in the female flower. Most CsCOL exhibited a diurnal oscillation pattern under different light treatment. Additionally, sequence analysis showed that CsCOL3 and CsCOL7 exhibited amino acid differences among the early-flowering and late flowering cultivars. Conclusion This study provided insight into the potential functions of CsCOL genes, and highlighted their roles in the regulation of flowering time in cannabis. Our results laid a foundation for the further elucidation of the functions of COL genes in cannabis.