The objectives of this study were to determine the physicochemical properties and antioxidant activity of red grape pomace powders (GPPs) from winemaking residue with particle sizes of >300, 250-125, 125-70, 70-38, and <18.83 pm. Superfine grinding treatment could decrease bulk density (from 0.40 to 021 kg/m(3)), tapped density (from 0.51 to 031 kg/m(3)), and fluidity (repose angle from 33.87 to 56.34 degrees and slid angle from 36.76 to 71.97 degrees, respectively) of GPPs, but improve the solubility (from 9.38 to 48.86%). The extract of GPP with a particle size of <18.83 mu m showed that highest total polyphenolic content (757.36 mg GAE/100 g) and flavanol content (19.46 mg CE/100 g) accompanied with the best antioxidant activity through all antioxidant assays (p < 0.05). SEM images revealed the shape and surface morphology of GPPs with different sizes. FTIR analysis showed that the superfine grinding did not damage the main structure of phenols as the powder particle size decreased. The results indicated that after superfine grinding treatment GPPs could serve as a potential resource of natural ingredients for food and nutraceutical application. (C) 2015 Elsevier B.V. All rights reserved.