Abstract CONSTANS ( CO) is a key gene in photoperiodic flowering pathway and locates between the circadian clock gene and the meristem identity gene. For elucidating the function of CO in flowering behavior of soybean, a CO-like gene, designated GmCOL4, was cloned from Glycine max cv. Kennong 18 using reverse transcription-polymerase chain reaction (RT-PCR) and bioinformatics methods. This gene encodes a protein embedded 2 conserved domains, B-box and CCT, which belong to subgroup III. Phylogenetic analysis based on critical amino acid sequences indicated that GmCOL4 is close to COL9 with similarity of 64.3%. The expression profiles of GmCOL4 revealed by quantitative real-time RT-PCR (qRT-PCR) showed a similar pattern to that of COL9. GmCOL4 was largely regulated by biological circadian, while light had weak effect on it. GmCOL4 was expressed mainly in leaves with the highest expression at anthesis stage. Therefore, GmCOL4 is one of the important genes for regulation of flowering in soybean.