Zinc oxide (ZnO) nanoparticles (NPs) are widely investigated for their antibacterial potential, yet their clinical translation is often limited by poor selectivity and safety concerns. In this study, ZnO NPs were surface-modified using carboxymethyl cellulose (CMC) to explore enhancements in antibacterial activity. The formation of the ZnO–CMC nanocomposite was confirmed through physical characterization techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and zeta potential measurements. The antibacterial efficacy of the CMC-modified ZnO NPs was evaluated in vitro against Lactobacillus acidophilus and Lactobacillus bulgaricus. Compared to unmodified ZnO NPs, the CMC-coated formulation exhibited increased antibacterial activity in a concentration-dependent manner. At 0.5% (w/v), bacterial viability reduction improved from 51% to 66%, and at 1.5% (w/v), from 63% to 77%. At a lower concentration of 0.1% (w/v), both formulations showed negligible effects. These results suggest that surface modification with CMC can enhance the antibacterial performance of ZnO NPs, potentially broadening their applicability in antimicrobial formulations.