In order to analyse the effect of small additions (up to 20 wt%) of low-density polyethylene (LDPE) on the crystallization kinetics and thermodynamics of an isotactic polypropylene (iPP), morphological studies of iPP/LDPE blends have been carried out. The results have shown that at LDPE percentages above 10% in the blend, the LDPE aggregates pass over the spherulitic limits and go into the intraspherulitic domains of the PP. The half-crystallization times (tau(1/2)) as well as the Avrami exponent (n) and the chain folding energy for PP crystallization (sigma(e)) increase markedly at LDPE percentages above 10% in the blend. The isothermal radial growth rate, G, of the PP in the blends is one-third of the plain polymer, although it remains constant at any blend composition. However, the overall kinetic rate constant seems to be influenced by the presence of the melt LDPE phase. In all cases, and according to the obtained results, an instantaneous nucleation takes place.