The effect of hydrophilic silica nanoparticles (SiO(2)) on the relaxation and breakup dynamics of selectively filled polyamide (PA6) droplets with different degrees of deformation in polystyrene (PS) matrix during quiescent annealing were in situ investigated. It was found that, with the increase of silica content, the relaxation process of PA6 droplets was slowed down gradually and the relaxation mode was changed correspondingly. The critical break aspect ratios (AR(cr)) of PA6 droplets were also improved with the increase in SiO(2) nanoparticle contents. Comparisons of the experimental values of AR(cr), characteristic relaxation time (tau(d)) and breakup time (tau(b)) of the SiO(2)-filled PA6 droplets with corresponding theoretical values were made. The results of comparison were discussed in terms of viscoelasticity and interfacial tension. It was proposed that the alternation of the viscoelastic properties of PA6 droplets in stead of the interfacial tension change of the blends was responsible for the phenomena observed. (C) 2011 Elsevier Ltd. All rights reserved.