The aim of this work is to determine the effect of draft ratio and twist level on core visibility ratios of dual-core yarns. For this aim, different types dual-core yarns containing PET/Elastane were produced under controlled conditions. To objectively evaluate the visual quality of the dual-core yarns, the frequency of the core filaments appearing on the yarn surfaces was counted on dyed knitted fabrics produced with these yarns by using image processing algorithm. The results showed that the draft ratio and the twist coefficient were the important factors influencing the core visibility ratios of dualcore yarns. It was found that the core covering performances of the pre-treated dual-core yarns produced with the lowest twist coefficient in the study were more incomplete than the others. Moreover, it was seen that the higher draft ratio on PET filament led to well wrapping of sheath staples to core filaments for dual-core yarns.