Abstarct: Given the complex drilling conditions in high-pressure and high-temperature environments, the development of novel additives to enhance the performance of water-baxsed drilling fluids is essential. In this study, nanocomposites baxsed on titanium dioxide nanoparticles with covalently bonded polymer chains, including polyacrylamide and a zwitterionic copolymer, were synthesized. These nanocomposites were prepared via aqueous radical polymerization and reverse mini-emulsion methods, and structural characterization tests indicated that the nanoparticles were well bonded to the polymer chains and exhibited uniform dispersion and desirable thermal stability. Performance evaluation of these materials in drilling fluids showed that the presence of the nanocomposites significantly reduced filtrate loss and filter cake thickness while improving the fluid’s rheological behavior. In particular, the increase in yield point and plastic viscosity, along with the maintenance of shear-thinning behavior, highlighted their effective role in enhancing the mechanical properties of the fluid. Rheological model analysis also indicated that the Herschel–Bulkley model provided the best fit compared to the power-law and Bingham models and had adequate capability in describing the flow behavior. Furthermore, the synthesized nanocomposites demonstrated considerable salt resistance and enabled the formation of dense filter cakes with low permeability. This feature was attributed to the synergistic effect between the titanium dioxide core and polymer chains, which reinforced the structural and functional properties of the fluid. The results of this study indicated that the designed nanocomposites can act as thermal stabilizers and filtration enhancers in water-baxsed drilling fluids, providing suitable performance under various temperature and pressure conditions. Therefore, they can be proposed as efficient additives for drilling fluids in complex drilling environments.