In this study, spacer knitted fabrics having electromagnetic shielding effectiveness have been developed by using various types of electrically conductive yarns. Shielding effectiveness of developed fabrics has been tested by standard ASTM 4935-10. The tests have been carried out at 100-1000 MHz frequency ranges. Analysis of variance and Multiple Comparisons methods have been used for evaluating the test outcomes. The test results indicate that the conductive yarn types and arrangement of these yarns in fabrics' structures significantly affect the shielding effectiveness of spacer knitted fabrics.