This paper discusses the effect of two co-products from lignocellulosic biorefineries on a typical Iowa subgrade soil in terms of laboratory measured strength and compaction properties. Emphasis is given to detailed data analysis of laboratory test results in comparing treated soils with untreated soils under different moisture conditions and additive concentrations. Results reveal that the bio-energy co-product (BCP) additives investigated in this study are promising materials to improve strength property of the typical Iowa soil classified to CL or A-6(8) for geotechnical applications. Especially, the co-product A containing higher lignin content is a more effective additive to reduce plastic property and optimum moisture content of soil.