Concerns about the cost, availability, and environmental impact of using petroleum-based materials have led to development of alternative asphalt binders for flexible pavements. The objective of this study is to investigate the feasibility of using wood lignin, a high-molecular weight powder, as an asphalt substitute or performance modifier. The rheological properties of the virgin asphalt and the lignin-asphalt blends were evaluated using laboratory performance tests according to Superpave specifications. Two types of asphalt binder (PG 64-22 and 76-22) and two lignin replacement contents (5% and 10%) were used in the experiment. It was found that the addition of lignin into the asphalt binder increased the viscosity of asphalt binder. The DSR test results indicate that the addition of lignin improves the rutting resistance of asphalt binder before or after the short-term aging process. However, the stiffening effect is less significant for the polymer-modified binder compared with the virgin binder, which suggests that lignin may chemically react with the cross-linking polymer molecule and does not purely act as filler. The BBR test results show that the addition of lignin does not significantly affect the susceptibility of the asphalt to thermal cracking. In addition, the separation tube test results indicate that the degree of separation varies among different binder types and lignin contents.