This study aims to investigate the geotechnical characteristics of three soils by adding waste plastics and a mixture of leaf ashes. The soil stabilizers used in the study are the plastics strips from waste plastic file folders and a mixture of ashes from five naturally occurring pozzolanic leaves in Sri Lanka. The plastics used in this study have a width of 5 mm and aspect ratios of 1, 2, 3, and 4 in the weight percentages 0.5, 1, 2, 4, and 8. The mixture of leaf ashes used is in the weight percentages 2, 4, 6, 8, and 10. The investigated geotechnical characteristics of the soils include the improvement of maximum dry density (MDD), optimum moisture content (OMC), soaked California bearing ratio (CBR), shear strength parameters, plastic index (PI), and Atterberg limits. The results suggest that the optimum improvement in soaked CBR and MDD can be achieved by adding 2% plastics and 6% leaf ash mixture into the soils. Shear strength parameters and PI can also be improved.