Sorghum bicolor (L.) Moench is known as a healthful food. We examined whether a water-soluble sorghum extract (SE) from S. bicolor has an anti-diabetic effect through a mechanism that improves insulin sensitivity or anti-adipogenesis. Although the treatment of SE did not affect the adipogenesis of 3T3-L1 adipocytes induced by isobutyl methylxanthine/dexamethasone/insulin (MDI), it significantly enhanced MDI/thiazolidinedione (TZD)-induced adipogenesis in 3T3-L1 adipocyte differentiation. Real-time polymerase chain reaction analysis showed that treatment with SE reduced the expression of adiponectin, adipocyte protein 2 (aP2), and resistin in 3T3-L1 adipocyte cells. SE suppressed the expression of transcription factors, peroxisome proliferator-activated receptor γ (PPARγ), and CCAAT enhancer-binding protein α in both MDI- and MDI/TZDs-treated 3T3-L1 adipocytes. SE treatment reduced tumor necrosis factor α protein in cell lysates from MDI-induced 3T3-L1 adipocytes but not those induced by MDI/TZD. Our results suggest that SE can serve as an effective food source that improves insulin sensitivity and an anti-obesity agent.