The study evaluated the influence of Costus lateriflorus bagasse fibre on the properties of expansive soils. Laterite and clay soil samples along Ubeta-Ula-Ubie road in Ahoada West LGA of Rivers state, Nigeria were prepared and subjected to laboratory analysis for swelling potential, volume change, maximum dry density (MDD), optimum moisture content (OMC), consistency limits, California bearing ratio (CBR) and unconfined compressive strength (UCS). Preliminary analysis classified the soils as A-7- 6 on the AASHTO classification system. Swelling potential, volume change, maximum dry density (MDD), liquid limit (LL) and plasticity index (PI) of the stabilized Laterite and clay soils along Ubeta-Ula-Ubie road decreased with increasing percentage of Costus lateriflorus bagasse fibre, while optimum moisture content (OMC), plastic limit (PL) and unconfined compressive strength (UCS) increased with the addition of Costus lateriflorus bagasse fibre. Results established that increase bagasse fibre content improved the properties of the soil suitable for road construction. However, the bagasse fibre performed better in Laterite soil than clay soil, and 7.5% bagasse fibre would be appropriate for use as stabilization material in soil with similar characteristics like the Laterite and clay soil along Ubeta-Ula-Ubie road.