Poly(acrylic acid), PAA, has been mixed in solution with silver nanoparticles, obtained by chemical reduction of silver nitrate. Two different sulfur-containing organic compounds have been used as stabilizers of Ag nanoparticles: mercaptosuccinic acid (MSA) and 3-mercaptopropionic acid (MPA). The formation of Ag nanoparticles has been monitored by UV-Vis spectroscopy. The morphology and composition of obtained nanomaterials has been studied by electron microscopy techniques (SEM/EDX and HR-TEM). Nanomechanical properties of nanocomposites (adhesion and nanohardness) have been investigated by Atomic Force Microscopy (AFM). Thermal stability has been determined using thermogravimetric analysis. The exposure of specimens to UV radiation allowed to observe the changes in the nanoparticle structure and to estimate nanocomposite photostability. MSA has proved to be a better stabilizer of Ag nanoparticles immediately after the synthesis, when MPA provides better storage stability. MPA has allowed for the creation of nanoparticles using mixed reduction (chemical/photochemical) of AgNO3. It has been found that the nanocomposite materials are stable for 12 months of storage in solution and in solid form.