This work presents an analysis of the parameters of cotton, polyester, and blended cotton/polyester yarns manufactured using PJ ring-, and BD 200S & R1 Rieter rotor spinning machines. Cotton/polyester blended yarns of 30 tex with a share of polyester fibres from zero to 100% were spun with the use of each of the selected spinning frames. We analysed the influence of the polyester fibre content in the blends on the structural parameters of carded and combed yarns with a constant twist coefficient.