Unbound aggregate materials are commonly used in highway bases due to their satisfactory mechanical strength and permeability. Compaction is the most important procedure in highway base construction, thus it is imperative to determine the best compaction method that does not significantly alter the gradation of the aggregates during construction. A laboratory study was undertaken to evaluate the vibratory and impact compaction methods on resilient modulus, bearing capacity, permanent deformation, and hydraulic conductivity characteristics of several aggregates. The results indicated that impact compaction increases fines content of aggregates, resulting in reduced permanent deformation and hydraulic conductivity. Impact compaction usually provides higher resilient modulus and increases the linearity of the resilient modulus curves as compared with vibratory compaction.