Major loci controlling flowering time and maturity of short-day plant soybean, E1, E2, E3, E4, E5, E6, E7 and E8, have been identified in soybean. The gene corresponding to E2 locus is a homolog of Arabidopsis GIGANTEA (AtGI). We identified three GI homologs in soybean and are verifying their roles in day-length dependent flowering. Expression anlysis indicated that GmGIs are ubiquitously expressed at all developmental stages of soybean plants. Diurnal expression of GmGIs fluctuates within light/dark cycles of long-day (LD) and short-day (SD). GmGI2 and GmGI3 have identical expression patterns under both day length conditions with the highest peak at zeitgeber time 8 h (ZT8) under LD and at ZT4 under SD. GmGI1 shows the peak at ZT12 under LD and at ZT8 under SD. All of GmGIs exhibit the earlier peak and the shorter phase under SD than LD. The results indicated that day length affects expressions of GmGIs. Subcellular localization analysis showed that GmGIs are mainly targeted to nucleus, similar to the localization of AtGI. Overexpression of GmGIs in Arabidopsis transgenic plants showed no significant effect on flowering time nor rescue of gi-2 mutant phenotype. The results suggested that GmGIs have different molecular functions in flowering time regulation of short-day plant soybean compared to long-day plant Arabidopsis. To investigate the molecular mechanisms of GmGIs’ functions in soybean flowering time control, we intend to identify target gene of GmGIs and interacting proteins by using yeast two-hybrid assay.