A comparison of the yarns spun on MJS and ring spinning system shows that both the tenacity and breaking elongation are higher for ring-spun yarn at all extension rates and gauge lengths. With the increase of polyester fibre content in blend, tenacity and breaking elongation increase with greater impact on air-jet spun yarn in majority of the cases. With the increase in extension rate, tenacity increases up to a certain limit beyond which a further increase in extension rate causes drop in tenacity. In short gauge lengths, the maximum tenacity is obtained at lower rate of extension than is tenable from the long gauge lengths. At very long gauge length (500mm), the tenacity of air-jet yarn shows no decrease with the increase in extension rate. As the gauge length becomes shorter the tenacity and breaking elongation increases for both types of yarn. The effect of change in extension rate and gauge length is more pronounced on air-jet yarn than ring-spun yarn and the F-ratio values on tenacity also reflect this. Breaking elongation increases with corresponding increase in extension rate and decrease in gauge length with some exception. Although the F-ratio values for breaking elongation show that the effects of change in these parameters are very much significant, no specific trend is obtained.