Metal and semiconductor nanoparticles have attracted much interest lately due to their unique size dependant properties, stemming from their quantum confinement effects and large surface areas. The main problem in nanoparticle synthesis is their aggregation which often prohibits tailoring of particle size. One of the convenient methods to manipulate and process these nanoparticles in technologically useful formulations is an “in-situ formation” of nanoparticles in polymer matrices which prevents the aggregation of the nanoparticles and enables their uniform distribution. The polyelectrolyte multilayers (PEMs) of polyallylamine (PAH) and polyacrylic acid (PAA) were assembled on hydrophilic polystyrene tissue-cultured and surface modified quartz substrates by alternately dipping the substrates into polyanion and polycation aqueous solutions with various pH values until the desired thickness of the PEMs was obtained. The linear charge density or concentration of free carboxylic acid repeating units of PAA was controlled by adjusting the pH of the dipping PAA solutions. Thus formed PEMs were exposed to the metal ion solution at nominally neutral pH. By subsequent reduction of Ag ions or sulfidication of the Zn ions, metallic (Ag) or semiconductor nanoparticles (ZnS) are formed within the PEMs. Since upon nanoparticle formation carboxylic groups of PAA are regenerated, the synthesis methodology can be repeatedly cycled to incorporate more metal ions, which enables the formation of nanoparticulate films where the nanoparticle size and concentration can be manipulated. The aim of this work is to control the size and concentration of the in-situ formed inorganic nanoparticles by varying the synthesis conditions.