With a surge in bacteria encroaching on our daily life, exacerbated antimicrobial resistance toward antibiotics, and sagacious short- and long-term responses of bacteria toward novel antibacterial nanoparticles, the need for developing rapid and effective antibacterial agents is increasing. Herein, Mo0.55W0.45O3–x samples are synthesized through a coprecipitation process, followed by annealing at 450–600 °C. Mo0.55W0.45O3–x samples showed outstanding activity after 10 min of incubation against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) under the compact fluorescent lamp irradiation; the activities were 98.948 ± 1.890 and 98.413 ± 1.080% for S. aureus and E. coli, respectively. The role of each reactive oxygen species (ROS) in suppressing bacteria was studied. The strikingly fast antibacterial rate was discovered with respect to semiconducting features of Mo0.55W0.45O3–x samples, including band positions, trap state, and band gap. We found that well-formed n-n heterojunctions and localized surface plasmon resonance (LSPR) excitation are responsible for antibacterial performance. Accordingly, we believe that a band position-considered system with numerous n-n heterojunctions and LSPR excitation will lead to efficient generation and separation of electron–hole pairs, facilitating the generation of ROS and subsequently resulting in the enhanced antibacterial performance.