Sustainable use of biomass as a renewable source of energy can be an alternative solution to the cost of fossil-based energy and global warming. Production of biofuel from plant biomass results not only in bio-based energy, but also in coproducts containing lignin, modified lignin, and lignin derivatives. This paper discusses the moisture susceptibility of subgrade soil stabilized by bio-based energy coproducts containing lignin, with the aim of establishing a new application for bio-based energy coproducts in soil stabilization. An experimental test program was conducted to compare the moisture susceptibility of lignin coproduct-treated soils and traditional fly ash stabilizer-treated soil samples. Additive combinations were also evaluated. There were two types of laboratory tests for moisture susceptibility evaluation: (1) unconfined compression strength (UCS) tests after "dry" and "wet" conditioning, and (2) visual observation of soaked specimens. Results indicate that the biofuel coproducts have excellent resistance to moisture degradation for the Iowa Class 10 soil classified as CL by the Unified Soil Classification System and as A-6(8) by AASHTO. In particular, Coproduct A with higher lignin content is more effective in providing moisture resistance than Coproduct B with lower lignin content as well as conventional additive (Class C fly ash). Moisture resistance comparable to that of Coproduct A could be obtained through the use of additive combinations.