A new theoretical fabric shear model has been presented and a quantitative study has been conducted on the shear properties of polyethylene(terephthalate) (PET) fabrics of four different fabric densities and five different weight reduction. The fabric shear properties were measured with KES-F handle measurement system. From the theoretical and experimerntal studies. following results can be summarized : 1) The fabric shear behavior is strongly dependent on the fabric density and free volume available for the constituent yarns and their filament. 2) Shear hysteresis at the small shear angle(2HG) is dependent more on the yarn tensile properties than on the fabric structure. 3) Shear hysteresis at the shear angle, 5$^{circ}$(2HGS) is dependent more on the interaction between two crossing yarns which is directly related on the fabric structure than on the yarn tensile properties.