No, whey protein isolate doesn't generally contain casein. Whey protein isolate is a purer form of whey protein, meaning it has had more of the fat, lactose, and other impurities removed. However, it is still made from the same dairy source as whey protein concentrate and may include some residual casein. If you are looking for a pure whey protein powder, you may want to consider whey protein hydrolysate, which is the most processed form of whey protein and contains almost no casein.