Objectives To evaluate the bioaccessibility of bioactive compounds present in Corn Bran using an in vitro gastrointestinal digestion model and to explore reducing particle size as a strategy to modify bioaccessibility. Methods Corn Bran (coarse and cryoground) was submitted to an in vitro digestion model of the upper gastro-intestinal tract. Supernatants of samples taken at different times of gastric and small intestinal digestion were analyzed by LC-MS to quantify phenolic acids and phytosterols. Undigested materials were acid hydrolyzed for 4 hours at room temperature and bioactive compounds quantified by LC-MS. Particle size and cell integrity of study materials were analyzed by Malvern Mastersizer 3000 Laser Light Diffraction Particle Size Analyzer and SEM, respectively. Results Average particle size of undigested coarse and cryoground Corn Bran materials was 645 μm and 62 μm, respectively. Microscopy revealed a very significant breakup of the cells in the cryoground material. LC-MS analysis confirmed high abundance of phenolic acids and phytosterols. There was minimal impact of particle size on in vitro bioaccessibility of most bioactive compounds tested. However, distinct bioaccessibility responses were observed. The release of phenolic acids happened during the small intestinal phase and it increased with time of digestion. The most abundant phenolic acid in Corn Bran, ferulic acid, showed very low bioaccessibility (<2%) at the end of digestion, likely representing the free (non-bound) fraction. Comparatively, higher release at end of digestion, was observed for coumaric (∼35%), vanillic (∼25%), sinapic and caffeic (both at around 20%) acids, and bioaccessibility of syringic acid was about 7%. In contrast, for Phytosterols (Campestanyl ferulate and Oryzanol-Campesteryl ferulate) about 60% release was observed at very early stages of the small intestinal digestion, and less than 20% release was measured at end of digestion which suggests chemical instability and/or transformation of these compounds in the digestion reaction. Conclusions In vitro bioaccessibility assessment of phytochemicals in Corn Bran demonstrated distinct release responses for different classes of compounds, indicating that the breakdown of digestive components of the Corn Bran matrix by the host enzymes differently impacts the rate of release. Funding Sources Cargill Inc.