This study assessed whether extracts of Kumamoto-grown Auricularia polytricha (AP) could suppress postprandial hyperglycemia. First, we assessed whether hot-water soluble, 76%-ethanol soluble and insoluble extracts (soluble dietary fiber; A-SDF) inhibited the carbohydrate-digesting enzymes alpha-amylase, maltase, and sucrase in vitro. A-SDF inhibited alpha-amylase. Thereafter, we performed oral loading tests in male Wistar rats, using the digestible carbohydrates starch, maltose, and sucrose. A-SDF decreased maltose-derived blood glucose levels. Furthermore, we found that the hardness and adhesiveness of A--SDF were greater than those of indigestible dextrin. These results suggest that A-SDF attenuates postprandial hyperglycemia.