We report on the experimental realization of all-dielectric planar chiral metamaterials (PCMs) with large optical activity (up to 26.5 degrees) in zeroth-order transmission under normal illumination. The design and fabrication processes are demonstrated in detail to show how to achieve the high-aspect-ratio, deep-groove, four-fold-rotational symmetric, subwavelength-period dielectric PCMs with prescribed polarization properties. The synchronization of numerical design and nanofabrication process appears to be an efficient, reliable and repeatable way to realize the PCM samples with high quality. (C) 2008 Elsevier B.V. All rights reserved.