In this PhD thesis pulsed laser ablation in water is used for synthesis of titanium dioxide and zinc oxide nanoparticles with strong photocatalytic properties. For that purpose the nanosecond laser ND:Yag with basic wavelength at 1064 nm is used. Various experimental techniques (XRD, XPS, TEM/SEM, UV-Vis, Raman) are performed for the purpose of characterization of synthesized nanoparticles in order to determine their crystal structure, optical properties, shape and size distribution. The simple method for determination of laser synthesized nanoparticles concentration in water is developed, in which the ablation crater volume and nanoparticles size-distribution data are used. The method is tested for titanium dioxide nanoparticles and verified by using Beer-Lambert law. Titanium dioxide nanoparticles are synthesized by pulsed laser ablation of titanium target and it is shown that they crystallized after heating in water at 90°C and developed large photocatalytic activity in the presence of UV and visible light when compared with P25. Photocatalytic efficiency of nanoparticles was calculated by measuring the photodegradation rate of different dyes (Methylene Blue, Rhodamine B) under UV or visible light and in their presence. A dependence of zinc oxide nanoparticles photocatalytic efficiency on their concentration, initial dye concentration and dye type was measured, and obtained relations are theoretically explained. The method for laser synthesis of doped nanoparticles is developed, in which pulsed laser ablation in water is used for ablation of target that is previously coated by dopant material using pulsed laser deposition. In this way the zinc oxide nanoparticles with different silver ratios are synthesized, and they are shown to have improved photocatalytic efficiency, which is the largest at the measured optimal silver ratio 0.32 wt %.