The study of yarn structure and related yarn properties has been the subject of much research. However, the study of the fiber packing density, which has practical significance for a number of yarns and their characteristics, has been limited to circular yarns because of the disordered yarn structure. In this paper, the fiber packing density of lyocell ring-spun yarns is determined with the image analysis method. This method does not have any limitation with regard to the fiber cross-sectional shape. The effect of yarn count, twist factor, spindle speed, traveler weight and front roller diameter on the fiber packing density in the yarn cross-section is analyzed. The results of this paper and the data published in other scientific works are in good agreement.