This research examined and compared grain, bran, and micronized bran samples of Ankor and Trego wheat stored at 25, 60 and 100^oC for their free radical scavenging properties, total phenolic content (TPC) and phenolic acid compositions. Bran and micronized bran samples stored at 100^oC showed decreased TPC and free radical scavenging activities over 9 days of treatment, while there was no significant change observed for grain samples. Because of smaller particle size, micronized bran was more sensitive to heat stress when compared to bran at the two elevated temperatures. In addition, extractable phenolic acids were increased during storage for all kinds of samples on a per dry weight basis. These results demonstrate that whole grain is a preferred form of long-term storage for better antioxidant preservation, and reducing particle size may accelerate the loss of natural antioxidants in wheat bran during storage and heat treatment.