Polycarbonate (PC)/mineral silica composites were prepared by melt-mixing to improve PC’s surface characteristics. The silica’s surface was modified using a silane coupling agent with amine functional moiety prior to blending. The effects of silica on the PC’s morphology, dynamic mechanical properties, molecular weight, and pencil hardness were investigated. Although SEM showed that silane treatment promoted interfacial adhesion between the PC and the silica, the storage modulus of the PC/silica composites increases with increasing silica content irrespective of silane treatment. Silica addition decreased the molecular weight (MW), and thus the melt viscosity of PC in the composites. The reduction was slightly greater at higher silica contents and when silane-treated silica was added. Despite the detrimental effects of silica on the MW, the pencil hardness of the PC increased to F grade when silane-treated silica of 40 phr was added possibly due to the increased modulus and interfacial adhesion.