In this study, stainless steel conductive yarns with 500 tex fineness and 14 Omega/m linear resistances were inserted into the reverse side of the knitted fabrics made from acrylic yarns. Six types of knitted fabrics with conductive yarns were produced on an E=7 gauge electronic flat bed knitting machine. Then the electromagnetic shielding efficiency (EMSE) of the sample fabrics were measured in the frequency range of 750 MHz - 3000 MHz. The EMSE variations of the sample fabrics having conductive yarns with respect to fabric structure and polarization type (vertical and horizontal) were also investigated. It was observed that the same samples showed different behaviors and have dissimilar EMSE values in different polarization conditions. When compared to horizontal polarization measurements, the vertical measurement results gave better EMSE values.