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Oxidation is the primary cause of long-term aging in asphalt pavements. As a pavement oxidizes, it stiffens and can eventually crack. The use of an antioxidant as a performance enhancer in an asphalt binder could delay aging and thus increase the life of an asphalt pavement. Lignin is a highly available, well-studied antioxidant. A wet-mill ethanol plant produces several coproducts, some containing lignin. The use of coproducts from ethanol production could benefit asphalt pavements while also providing more value to the coproducts. Four lignin-containing coproducts were combined with four asphalt binders in varying amounts to discover the optimum amount of coproduct that would provide the greatest benefit to the asphalt binders. The asphalt-coproduct blends were evaluated according to Superpave® specifications and performance graded on a continuous scale. The data indicate a stiffening effect of the binder caused by the addition of coproduct–the more coproduct added, the greater the stiffening. Binder stiffening benefits the high-temperature properties, while the low-temperature binder properties are negatively affected. However, the low-temperature stiffening effects are small. Instead of acting purely as a filler and shifting the temperature range, the lignin has an overall effect of widening the temperature range of the binders. Testing reveals that the lignin in the coproducts benefits the intermediate-and low-temperature properties of the binders. Oxidative aging products were evaluated and some antioxidant effects were noticed.