As we have reported, flaxseed lignan, (+)-secoisolariciresinol (SECO), (-)-SECO, and meso-SECO were stereoselectively synthesized and their biological functions were evaluated. In the present study, we focused on the effects of SECOs on the regulation of 3T3-L1 adipocytes, and identified the structure-activity relationships. Optically active SECO and meso-SECO were tested for their effects on lipid metabolism in 3T3-L1 adipocytes. (-)-SECO accelerated adiponectin production of 3T3-L1 adipocytes. On the other hand, (+)- and meso-SECO suppressed the production of adiponectin. In addition, triglyceride (TG) accumulation in 3T3-L1 adipocytes was significantly suppressed by all three SECOs tested here, as was 17beta-estradiol, when the SECOs were added to the medium during induction of 3T3-L1 preadipocytes to adipocytes. Especially, (-)-SECO strongly reduced TG accumulation. It is well-known that SECO has estrogen-like activity. Hence the estrogen-like activity of each SECO compound was assessed. Only (-)-SECO had estrogen-like activity.