Yes, soy protein powder can expire. Like any food or supplement product, it's important to check the expiration date and to store it properly to maintain its freshness and potency. It's recommended to store soy protein powder in a cool, dry place, and to always use a clean utensil when scooping it out to avoid contamination. If the powder has an off smell or taste, or if there is any visible mold or discoloration, it should be discarded.