Abstract: Roads construction projects require large quantities of suitable soils as a filling material. However, in urban areas, when roads are constructed, suitable filling soils have to be hired with enormous costs. Thus main objective of this research was to stabilize weak subgrade soils mixing with fly ash and rice husk ash. Weak sub-grade soil was obtained from Mahokanda construction site in Matara, Sri Lanka. Fly ash and rice husk ash were obtained from Lakvijaya power plant in Puttalam and rice mills in study area, respectively. Forty-eight weak subgrade soil samples were mixed with stabilizers (fly ash and rice husk ash) in different ratio and then 16 specimens were cured for 7 days while other 32 (2X16) samples were cured for 14 and 28 days, respectively. In order to find out maximum strength of each soil sample, different soil tests viz Atterberg Limits, Proctor Compaction, Swell Index (SI) and California Bearing Ratio (CBR) were carried out. Results revealed that maximum CBR value (36.01%) was obtained, when 70% of soil blends with 20% of fly ash and 10% of rice husk ash at 28 days curing period. Reason for the increment of CBR may be due to formation of cementitious compound in the mixture is due to chemical reactions of SiO2 in stabilizers and CaOH present in soils. Based on results, policy implications are discussed in relation to need of stabilizers in road construction projects in order to improve stabilizing weak subgrades while decreasing project cost and utilizing waste materials.