Optical activity and cross polarization conversion (CPC) of a rotated-arm-square chiral metamaterial (CMM) is reported in this work. Proposed CMM shows strong chirality owing to the cross coupling between the induced magnetic field and incident electric field of the applied electromagnetic wave. Mechanism of CPC functionality is explained based on the surface current distribution of CMM structure. Microwave experiment is performed to reveal the CPC utility of the proposed CMM. Among various designs on the CPC converters, possibility of near 99% efficiency is revealed in the proposed CMM. © 2013 AIP Publishing LLC.