The industrial sector is increasingly interested in the production of yarns based on renewable, efficient, innovative, and ecological resources. Among these precursors, cellulose nanofibrils (NFC) have gained attention due to their interesting characteristics for the development of new products. However, their dimensions pose challenges in their use. Therefore, this study aimed to analyze the influence of NFC concentrations and dimensions on the quality of bicomponent yarns. The bicomponent yarns were produced using a coaxial needle and the dry–wet-spinning method. The outer layer was made of guar gum (3 % w/v) and the inner layer of NFC bleached at two different degrees of refining (NFC A and NFC B). Yarn production involved varying concentrations of NFC (4.5 %, 3.5 % and 2.5 % w/v) NFC, which were characterized by real density analyses, tensile strength, water absorption, thermogravimetry, and scanning electron microscopy. Guar gum showed more hydrophilic characteristics, and its delay in hardening caused a less circular section and flaps on the side of the yarn. NFC B exhibited the smallest average diameter, and higher concentrations resulted in yarns with greater mechanical strength, more circular cross-sections, and fewer microstructural defects.