Abstract The integration of direct bandgap III-V materials on Si is one of the main tasks on the way to the development of cheap and highly effective optoelectronic devices. The goal of this work is to study the morphology and optical properties of GaAs nanoparticles grown on Si(111) by molecular beam epitaxy (MBE). Nanostructure morphology is studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optical properties are studied by photoluminescence (PL) and Raman spectroscopy. Interestingly, despite large lattice mismatch between the silicon substrate and GaAs no sufficient change of Raman spectra was observed for both continuous layer and nanoparticles indicating that they are relaxed. The room temperature PL signal in the red spectral range was obtained from the epitaxial structure. It is demonstrated that high pump optical excitation of the nanostructures can lead to sufficient change of the PL signal typical for photo-oxidized GaAs.