In this study, to stabilize problematic silty sand soils, Microsilica-Lime admixture was used as an additive. Various samples containing 0, 1, 2, 5, 10 and 15% (by weight) Microsilica and 0, 1, 3 and 5% (by weight) Lime were prepared. To investigate the role of the studied additives on the stabilization of the sandy soils, unconfined compressive strength of the materials and their swelling potential, were considered. To do this, unconfined compressive strength test, California Bearing Ratio, also, swelling tests were carried out. As a result, the unconfined compressive strength of samples with 10% Microsilica and 3% Lime in curing time of 28 days was obtained about 50 times larger than the strength of the untreated samples. On the other hand, the samples stabilized only with 1% Lime showed considerable swelling potential while adding only 1% Microsilica caused a considerable reduce in the amount of swelling. Unconfined compressive strength of samples containing 1% Microsilica and 1% Lime was about 12 times larger than the strength of the untreated samples and these samples showed less swelling potential. Then, these amounts are considered as the optimal amounts, which are used in the road construction projects. Also, the results obtained from scanning the samples using electron microscope illustrated that the Microsilica causes to form crystalline micro-structures in the soil which is the main cause for increasing the strength of stabilized samples.