The production and use of biofuel have increased under the context of sustainable development. Biofuel production from plant biomass not only produces biofuel or ethanol but also coproduces products containing lignin, modified lignin, and lignin derivatives. The use of lignin-containing biofuel coproduct in pavement soil stabilization was explored as a new application area. The primary experimental test plan encompassed the comparison of coproduct-treated soils, untreated soils, and traditional stabilizer-treated soils in terms of their strengths. The focus of the secondary experimental test plan was to investigate the effect of additive combinations on strength improvement. The laboratory test matrix in each test plan included variations in additive type, additive content, curing period, and moisture condition. Statistical analyses were performed on unconfined compression strength test results to evaluate whether the strength improvements resulting from the addition of the coproducts to soils are significant. Results indicated that the biofuel coproducts are effective in stabilizing the Iowa Class 10 soil classified as CL or A-6(8). Strengths comparable to traditional additive (fly ash) could be obtained through the use of combined additives (Coproduct A  fly ash; Coproduct A  Coproduct B). The use of biofuel coproduct as a stabilization material for soil appears to be one of many viable answers to the profitability of the biobased products and the bioenergy business.