in this study, the effects of vacuum steaming process parameters (temperature and duration) on tenacity properties of 100% cotton and 100 % viscose yarns were studied. For this purpose, the yarns with different twisting coefficients and numbers were twisted and exposed to vacuum steaming at different temperatures and for durations appropriate to their raw material properties. Tenacity properties of the yams were measured before and after vacuum steaming. The results obtained were assessed by means of SPSS statistical analysis program. Variation analysis and SNK test were carried out at 5% (0.05) level of significance. As a result of this study, it can be inferred that vacuum steaming temperature has significant effect on tenacity properties of 100 % cotton and 100 % viscose yarns but vacuum steaming duration has been found to be statistically insignificant on tenacity properties of cotton yams, and viscose yams.