This study was performed in order to investigate the effects of tandem and conventional vacuum steaming on the physical properties of 100% cotton and 100% viscose yarns. The yarns with different twisting coefficients and numbers were twisted and exposed to tandem and conventional vacuum steaming at different temperatures. Tenacity, unevenness, hairiness, twist liveliness, package hardness values, and spirality of knitted fabrics produced from these yarns were measured before and after vacuum steaming. The results obtained were assessed by means of COSTAT statistical analysis program. Variation analysis and SNK test were carried out at 5% (0.05) level of significance.