An optimal design experimental method that can accurately measure the optical activity of the periodic planar chiral structure sample is proposed.This me thod is based on an optical test system mainly consisting a precise stepping motor and a fiber optical spectrometer.In addition,the optical activity of the periodic planar chiral st ructure is performed through detailed deduction of the formula and theoretical analysis.Th e analysis results reveal that when the linearly polarized light transmits through the peri odic planar chiral structure the polarization azimuth rotation angle is a functi on of the polarization angle of the incident light,since the 90°-rotation symmetry is broken caused by the random errors of manufacture.Experimental results exactly demonstrate the validity of theory anal ysis.The optical activity of the periodic planar chiral structure sample fabricated by el ectron beam lithography technology is measured by the designed optical test system.The expe rimental results show that the periodic planar chiral sample possesses the optical activi ty of 0.05° at the wavelength of 633nm.As a consequence,the optical activity of the fabricated c hiral structure is well demonstrated.