Technical Abstract: Oat bran concentrate (OBC) was defatted by supercritical carbon dioxide, pin-milled and air classified into five fractions (less than 15 micrometer, 15-18 micrometer, 18-24 micrometer, 24-30 micrometer and greater than 30 micrometer). Beta-glucan content (% dry weight) of defatted OBC, its subsequent pin-milling, and the air classified fractions in ascending particle size was 14.3, 17.0, 4.3, 5.8, 12.6, 14.7, and 22.4, respectively. High-performance size-exclusion chromatography equipped with multi-angle laser-light scattering and refractive index detectors showed amylopectin was the predominant molecule present in all OBC powders, but was present in greater concentration in fractions collected that were less than 24 micrometer. Fractions greater than 24 micrometer, which had the highest beta-glucan contents had higher starch gelatinization temperatures (measured using a differential scanning calorimeter), and had substantially higher peak, breakdown, final and setback paste viscosity (measured using a Rapid Visco Analyzer) compared with the other lower-beta-glucan containing fractions. No differences in water retention of 25% (w/w) oat powders in water (measured using thermogravimetric analyzer) were observed among defatted OBC, its subsequent pin-milling, and the five fractions separated by air classification. In particular, differences in pasting properties shows that defatted, pin-milled OBC that is fractionated by air classification will have different food applications depending on particle size collected.