Sodium-ion batteries (SIBs) have garnered significant attention as a cost-effective and sustainable alternative to lithium-ion batteries (LIBs) due to the abundance and eco-friendly extraction of sodium. Despite the larger ionic radius and heavier mass of sodium ions, SIBs are ideal for large-scale applications, such as grid energy storage and electric vehicles, where cost and resource availability outweigh the constraints of size and weight. A critical component in SIBs is the electrolyte, which governs specific capacity, energy density, and battery lifespan by enabling ion transport between electrodes. Among various electrolytes, composite polymer electrolytes (CPEs) stand out for their non-leakage and non-flammable nature and tunable physicochemical properties. The incorporation of NASICON (Na Super Ionic CONductor) fillers into polymer matrices has shown transformative potential in enhancing SIB performance. NASICON fillers improve ionic conductivity by forming continuous ion conduction pathways and reduce polymer matrix crystallinity, thereby facilitating higher sodium-ion mobility. Additionally, these fillers enhance the mechanical properties and electrochemical performance of CPEs. Hence, this review focuses on the pivotal roles of NASICON fillers in optimizing the properties of CPEs, including ionic conductivity, structural integrity, and electrochemical stability. The mechanisms underlying sodium-ion transport facilitated by NASICON fillers in CPE will be explored, with emphasis on the influence of filler morphology and composition on electrochemical properties. By scrutinizing the recent findings, this review underscores the potential of NASICON-based composite polymer electrolytes as appropriate material for the development of advanced sodium-ion batteries.