Noble metals nanoparticles prepared by laser ablation in water. The structural and optical properties of the Ag and Au nanoparticles investigated using (UV-Vis) spectrophotometer and TEM. The produced nanoparticles show small and sharp plasmon peaks around 400nm and 500 nm for silver and gold respectively. The nanoparticles have spherical shape with average size of about 30 nm. The effect of gold and silver NPs was studied on the activity of acid phosphatase (ACP) in blood sera of healthy subjects. The result correlated with the observation that gold and silver nanoparticles had inhibition effect on serum acid phosphatase activity, and this effect increased with increasing the concentration of the nanoparticles.