Abstract: Oedometer expansion and direct shear tests are conducted on expansive soil with various initial water contents. Expansive force and shear strength of the samples with/without vetiver roots with different initial water contents are measured. The expensive force and shear strength with respect to reinforcement of vetiver roots are investigated. It is illustrated that vetiver root can increase shear strength and be used as flexible reinforcement to control expansive deformation and release expensive force of expansive soil with a degree of saturation under rainfall.