The need for highly stretchable fabrics with good and lasting handle properties such as absorbance, feel, and comfort has inspired researchers to constantly involve in blending of natural and artificial fibers.One of the commonly used methods of blending is core yarn spinning.Core spun yarn structure consists of two components; the sheath and the core. Normally, a continuous multifilament yarn is used as a core while cotton staple fibers are used to cover the filament.Cotton staple fibers have been a favorite choice for the sheath of core spun yarns because of their aesthetic properties.Ring spinning is considered the traditional spinning methods.With improving technology, ring spinning method has been modified in different ways to fit production of different kind of yarn structures.One of the structures is core spun yarn.　　Since T-400 has outstanding properties including among others, chlorine resistance, good elasticity and soft handle, blending it with cotton would hence achieve a good yarn suitable for production of fabrics which can find use in different textile applications such as sports garments as well as applications where stretch and comfort is highly required.　　In this research, we focused on optimization of spinning parameters of T-400/cotton yarn and further studies were made on the fabric knitted from the yarn that was produced using optimum parameters.Quadratic general rotary unitized design method was used in this study, to design experiments and analysis was done by mat lab to determine the optimum values.　　T-400 is a bi-component filament based on sorona 3GT polymer form DuPont.In our research, an experimental design was generated which included three factors and five levels.The factors considered for optimization include, twist, filament draft and the spindle speed with respect to the yarn properties tested by Uster tester.The optimum spinning parameters for Hairiness, Evenness and tenacity while holding other yarn qualities as limiting factors were; twist factor 430, filament draft of 0.945 and the spindle speed of 7494 rev/min.　　The study successfully determined the optimum spinning parameters for a T-400/cotton core spun yarn.The yarn produced was then used to produce a plain knitted fabric using a circular knitting machine.　　Properties of plain knitted fabric made from 100％ cotton ring spun yarn were compared with one made from Cotton/T-400 (70.4C/29.6T).We focused on knitted fabric properties such as the bursting strength, elongation at break, tensile strength, air permeability as well as pilling properties.Fabrics were then knitted using a circular machine, for consistence of results plain knit structure was adopted for all samples.Knitted fabric properties were then tested and results statistically analyzed.Research results show that, plain knitted fabrics made from Cotton/T-400(70.4C/29.6T) ring core spun yarn exhibit better elongation at break, bursting strength and air permeability.Whereas the fabric made from 100％ cotton showed better pilling resistance and tensile strength compared to Cotton/T-400 (70.4C/29.6T) plain knitted fabric.