The efficiency of heterogeneous nucleation of isotactic polypropylenes (iPP) with various isotacticity and MWD is estimated by an increase of the crystallization temperature (T-cr). A bi-component nucleating system, composed of a pimelic acid and a calcium stearate, was added to the polymeric matrix in the molten state. The relative increase of T-cr is found to be independent of the structure stereo-regularity of iPP. On the contrary, dependent on the polymer structure, the investigated nucleating system influences in a different way the creation of the beta-phase. The form of the DSC melting curves, for the beta-phase rich iPP samples, is discussed in terms of various preliminary cooling conditions. The transformation from a multi-modal form of the DSC melting peak to a simple one is related to the lowering of the cooling rate and to the increase of the heating rate.