Hierarchical Ag/TiO₂ composites were successfully synthesized via a hydrated magnesium carbonate hydroxide template-induced route. The prepared composites possess hierarchical flower-like structure and high Brunauer–Emmett–Teller (BET) surface area of 131.9 m² g⁻¹. The amount of silver nanoparticles (Ag NPs) with diameter of 20–40 nm in the composite can be adjusted by the concentration of AgNO₃ solution. The antibacterial potency of Ag/TiO₂ composites was investigated against Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus) by determining the minimal inhibitory concentration (MIC), the growth curve of bacteria and using the zone of inhibition technique. The synergistic effect of Ag NPs and TiO₂ lead to superior and long-term antimicrobial activities of the composites with a bacteriostatic rate as high as 99.99%. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the fluorescence microscopy showed the integrity of membrane of the bacteria was destroyed by adding a given amount of composites resulting in cell death as well. The mechanism of antibacterial activity of composites was also taken into account by using TEM, inductively coupled plasma atomic emission spectrometry (ICP-AES), ultraviolet visible diffuse reflectance spectroscopy and fluorescent microscopy.