 Alumina micro-spheres with mesoporous structure called porous aluminium oxide (POA) were prepared through a hydrothermal method using Al2(SO4)3·18H2O followed by a thermal decomposition process. Silver nanocomposites of POA (Ag/POAs) with high biochemical activity were synthesized by sorption of silver nanoparticles in the matrix of POA. Synthesis of Ag/POAs using photochemical reduction enables the producing silver nanoparticles preventing their aggregation. Ag/POAs demonstrated a stronger bactericidal activity than POA. The colony-forming ability of Escherichia coli was completely lost in 1 day on Ag/POAs at silver nanoparticles concentration of 0.241 ppm. Staphylococcus epidermidis displayed higher tolerance to Ag/POAs at all silver nanoparticles concentrations, the growth of Staphylococcus epidermidis was stopped at concentration of 0.374 ppm. The bactericidal activity of Ag/POAs against bacteria in drinking water was found to be highly effective, the growth of bacteria was completely lost in 1 day at silver nanoparticles concentration of 0.108 ppm.