This investigation aimed to determine the effect of spinning system, yarn count and twist multiplier and their interactions on single yarn mechanical properties. Also, the Stress-Strain curves were plotted with the yield points and breaking points and their corresponding yarn properties (toughness, stiffness and Initial Young Modulus) were derived and calculated. As well as, the relative importance % of three spinning factors toward the single yarn mechanical properties was measured.Resultsrevealed that the main effects of spinning factors i.e. spinning system, yarn count and twist multiplier were generally significant or highly significant on all single yarn mechanical properties except stiffness and initial Young's modulus. Regarded the first and second order interaction effects, they were no significant for all single yarn mechanical properties indicating that each one of the three spinning factors reflected similar behavior under the other two factors. It is obtained that the compact and ring spinning systems produced yarns are markedly stronger, good elasticity and more durable than the yarns spun by open-end system. Result indicates that finer yarns are weaker and have lower extension at break than coarser yarns. It is obvious that yield strain, breaking extension, breaking tenacity and toughness significantly increased as a result of increasing the twist multiplier from 3.5 up to 4.5. Results exhibited that the spinning factors explained the most single yarn mechanical properties variation expressed as coefficient of determination (R²). The maximum relative importance % was obtained by yarn count followed by twist multiplier for yield strain, yield stress and breaking extension while the spinning system was the second important factor for breaking tenacity and toughness. On the other hand, it is appeared that the studied spinning variables accounted for least and ineffective part of the variation of stiffness and Initial Young's Modulus.