A new experimental setup designed to monitor by atomic force microscopy (AFM) the time evolution of a single micrometer-sized polymer spherulite during crystallization at elevated temperatures is presented. For the case of blends of poly(aryl-ether-ether-ketone), PEEK, with poly(ether-imide), PEI, it is shown how AFM can help visualizing the time sequence and space location of events occurring during polymer crystallization, specifically growth, branching and thickening of lamellar stacks (fibrils). This method complements other non-destructive techniques, e.g. optical microscopy, as it is able to examine the growth of very small crystals occurring for high degrees of supercooling. In addition, not only the overall spherulitic growth rate but also the growth rates of individual fibrils could be evaluated. The potential of the technique to evaluate crystallization near the surface by following the evolution of the surface roughness is briefly discussed.