This study aims to predict the strength and elongation properties of cotton/polyester blended rotor yarns, using blend ratios and yarn count as predictors. A simplex lattice design with two replications at each design point is constructed to determine the combinations of the fibres' mixture ratios. Prepared cotton/polyester blended slivers were used to produce rotor yarns with five different counts on a laboratory-type rotor spinning machine (quickspin). Based on experimental observations, mixture process crossed regression models with two mixture components and one process variable (yarn count) are constructed to predict strength and elongation properties. All statistical analysis steps are performed on Design-Expert statistical software.