N,N'-Dicyclohexyl-2,6-naphthalenedicarboxamide (NJS) is an efficient nucleating agent to prepare isotactic polypropylene (iPP) samples rich in the beta-modification (beta-iPP). However, NJS is not a selective beta-nucleating agent, as the related samples always contain both alpha and beta modification of iPP. Depending on the final temperature of heating (T-f), NJS may be partially or completely dissolved in the iPP melt. The dual nucleation ability of NJS was studied by polarized light microscopy (PLM) and calorimetry (DSC). It was established that the lateral surface of the needle crystals of NJS acts as alpha-nucleating agent. Because of the solubility and dual nucleating ability of NJS, a wide variety of supermolecular structures may form in its presence. The feature of the structure formed during the crystallization of iPP depends on the concentration of the nucleating agent, on the end temperature of heating, and on the thermal conditions during cooling and crystallization. In this study we observed an alpha beta-transcrystalline layer development on the lateral surface of the needle crystals of NJS, dendritic and microcrystalline structures, and a spectacular "flower"-like agglomerate of beta- and alpha-crystallites. A model was proposed to explain the dual nucleating effect of NJS.