In this work, the effect of optimum drafting condition on the drafting behavior and yarn quality of the bamboo charcoal-modified fiber blended spun yarns were studied. We measured the drafting force and drafting force variance, CV% of the bamboo charcoal-modified Polyester/Cotton (BCP/C) blended roving and bamboo charcoal-modified Rayon/Cotton (BCR/C) blended roving to examine the influence of the roller gauge and drafting ratio on drafting behavior and yarn quality. We understand that the drafting force of the bamboo charcoal-modified fiber blended roving follow the same trend as that for the regular P/C and R/C blend roving. However, the drafting force presents some difference in characteristics between these bamboo charcoal-modified fiber blended rovings. To correlate the drafting force variation, CV% and the bamboo charcoalmodified fiber blended spun yarn properties, we evaluated the yarn quality and investigate the yarn quality index in conjunction with the break drafting ratio. Therefore, in this work, we can obtain the best optimum drafting conditions for bamboo charcoal-modified fiber blended spun yarns; for the 19.7 tex of BCP70/C30 blend spun yarn was under the roller gauge of 54 mm at the draft ratio of 1.3, whereas, for the 19.7 tex of BCR40/C60 blend spun yarn was under the roller gauge of 54 mm at the draft ratio of 1.2.