Photodecomposition by pulsed ultraviolet laser irradiation of copper acetylacetonate (CuAcAc) crystals which were embedded in polymethylmethacrylate (PMMA) films has been investigated by scanning (SEM) and transmission (TEM) electron microscopy. Crystal structure and the phase composition before and after irradiation were also characterized by electron diffraction and X-ray photoelectron spectroscopy (XPS). The photodecomposition occurs at and above a laser fluence threshold and yields particularly the formation of metallic copper clusters with an average size of 10-30 nm.