Transparent nanocomposite films were fabricated by blending a concentrated nanocomposite formed by in-situ polymerization of polycarbonate in the presence of alumina nanowhisker with a high molecular weight polycarbonate. Polycarbonate was grafted to the alumina nanowhisker surface to improve nanofiller dispersion and load transfer to polymer matrix. Fourier transform infrared spectroscopy confirmed the functionalization of the nanowhisker with polycarbonate. Samples produced using functionalized alumina exhibited improved dispersion compared to the raw alumina nanowhiskers in the PC. Functionalization of alumina nanowhisker enhanced tensile properties (Young's modulus and tensile strength) relative to the pure polycarbonate and blends produced with raw alumina nanowhisker. Additionally, the nanocomposite formed using in-situ polymerization showed small decreases in transparency in the visual range compared to the base polymer with increased absorption in the UV range. The effect of reaction temperature during in-situ polymerization on the properties of the nanocomposite was investigated. Higher reaction temperature resulted in improved dispersion and sharp increases in tensile modulus and shear strength.