Prussian blue (PB) nanoparticles were synthesized by two methods from FeCl2 and K3Fe(CN)6 and from FeCl3 and K3Fe(CN)6 based on the method published by Fiorito et al., and stabilized by different polymers like polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyallylamine hydrochloride (PAH), polydiallyl-dimethyldiammonium chloride (PDDA) and polystyrene sulfonate (PSS). The effect of the monomer/Fe3+ ratio was studied regarding the average particle size and zeta-potential. The forming PB structure was checked by X-ray diffraction. The stabilization was successful for every applied polymer, but the average particle size significantly differs. Particle size distributions were determined by Malvern type nanosizer equipment and by transmission electron microscope (TEM) and zeta potential values were determined for the obtained stabile samples. The results revealed that by using FeCl2 and K3Fe(CN)6 for PB preparation particles with narrow size distribution and average diameter of 1.7 nm occurred but stabilization was necessary. By the other method the dispersion was stabile with 182 nm particles but the particle size exponentially decreased to 18 nm with increasing PVP concentration. Ultrathin nanofilms were prepared on glass support by the alternating layer-by-layer (LbL) method from PB particles and PAH. The morphology of the prepared films was investigated also by AFM. The films were immobilized on interdigitated microsensor electrodes (IME) and tested in sensing hydrogen peroxide and different acids like acetic acid, hydrochloric acid vapors.