Nanoparticle production by Cu(acac)2 vapour decomposition was studied. The composition of the produced particles varied from Cu to Cu2O depending on experimental conditions. In order to explain the crystalline phase behaviour, a kinetic model to build a semiempirical dynamic phase diagram of the products was proposed. Prevailing role of copper dimers in the processes of copper and copper (I) oxide particle growth was demonstrated. The composition of products was determined by reactions on the surface of growing particles and depended on the ratio of gaseous species. The calculated dynamic phase diagrams were in excellent agreement with the experimental results.