<p>Carrageenan fibers produced via wet spinning have attractive applications with excellent flame-retardant properties but suffer from limited mechanical strength, hindering broader applications. This study investigates the effect of cellulose nanofibril (CNF) reinforcement on the mechanical and morphologic properties of kappa-carrageenan (k-CAG) fibers. Two types of CNFs—pristine CNF (PCNF) and TEMPO-oxidized CNF (TOCNF)—were incorporated at 1–5 wt%. Optimized wet-spinning conditions included 2-N sodium hydroxide as the dissolution solvent, 8-wt% k-CAG, 5-wt% CaCl₂ or BaCl₂ as coagulation baths, and ethanol as the washing solvent. SEM revealed that CNF addition increased surface roughness and wrinkling, particularly in PCNF-reinforced fibers. The choice of crosslinking cation significantly influenced fiber properties: Ca²⁺ crosslinking led to larger diameters, lower tensile strength, and higher elongation at break, whereas Ba²⁺ crosslinking resulted in stronger, more compact fibers. Notably, in BaCl₂-coagulated fibers, tensile strength increased from 2.76 to 5.03&#xa0;cN/dtex with 5-wt% PCNF, marking the highest reported strength for CAG fibers. In contrast, TOCNF reinforcement showed minimal mechanical enhancement. This study highlights the potential of PCNF for reinforcing k-CAG fibers and provides insights into how CNF type and coagulation bath composition affect mechanical performance. These findings pave the way for developing sustainable, high-performance biopolymer fibers for advanced applications.</p>