Alumina micro-spheres with mesoporous structure called porous aluminum oxide (POA) were prepared through a hydrothermal method using AI2(SO4)3·18H2O followed by a thermal decomposition process. Nanocomposites with high biochemical activity were synthesized by sorption of silver nanoparticles in the matrix of POA. Silver nanocomposites of POA (Ag/POAs) were effective against both Gram-negative and Gram-positive bacteria, Escherichia coli and Staphylococcus epidermidis.