Oat hull ethyl acetate extract (50 mu g/mu L) significantly inhibited triglyceride accumulation in 3T3-L1 adipocytes without causing cytotoxicity. The major active compound in the extract was isolated and identified as 5,7,4'-trihydroxy-3',5'-dimethoxyflavone, tricin by mass spectrometry and 1H and C-13 NMR analyses. The tricin content in oat hull was approximately 18 mg/kg dry weight, and tricib constituted 9.6% of the total phenolic compounds in oat hull extract. The treatment of 3T3-L1 cells either with extract or purified tricin resulted in decreased lipid accumulation. The extract significantly decreased the activity of glycerol-3-phosphate dyhydrogenase, a marker of adipocyte differentiation in a dose dependent manner. The expression of major transcription factors, such as peroxisome proliferator-activated receptor (PPAR)-gamma, CCATT/enhancer binding protein-alpha (CEBP/alpha), sterol regulatory binding protein 1 (SREBP1) and fatty acid synthase (FAS) was also significantly suppressed by the extract. When commercial purified tricin was added to 3T3-L1 cells the expression of all transcription factors were significantly decreased as low as 1.5 mu g/mu L treatment. These results suggest that oat hull extract containing tricin possesses anti-adipogeneic effect. (C) 2015 Elsevier Ltd. All rights reserved.