This paper presents investigations on the influence of arecanut husk ash and water hyacinth stem ash as an additive on the plasticity behavior of soil. Ashes are mixed with the soil at 5, 10, 15 and 20 wt%. It is observed that the arecanut husk ash has decreased the plasticity index, whereas water hyacinth stem ash has increased the plasticity index with the increase in ash content. For finding minimum plasticity value, 15% addition of ANA can be considered as the optimum level. Keywords:lateritic soil; liquid limit; areca nut husk ash; water hyacinth stem ash Nomenclature: ANA:arecanut husk ash; WHA: water hyacinth stem ash; ISSCS: Indian standard soil classification system