The effects of fiber characteristics such as fiber length, fineness, and bundle strength in the cotton fiber mixture of multimodal distribution on the properties of ring spun cotton yarn have been studied. The relationship between the fiber properties including fiber quality index and the yarn properties including yarn quality index has been studied by mill spinning experiments using 1 bale and 40 bales differing in weight proportion and in fiber properties of the individual bales. Multiple linear regression analysis of the relationship between the fiber properties and the cotton spun yarn properties produced from mill scale experiments showed that strength, elongation, toughness index, and yarn quality index of spun yarn increased with fiber quality index, but that the irregularity of spun yarn decreased with fiber quality index. In addition, it showed that there was no significant relationship between the fiber quality index and the stiffness index of the spun yarn. The determination coefficients of the multiple linear regression equations between fiber properties and yarn properties such as lea strength and count strength product are larger than those of the multiple linear regression equations between fiber properties and yarn properties such as single yarn strength and tenacity.