Morphology development during the coalescence under shear in polypropylene/polystyrene blends was studied in this article. The coalescence was performed by decreasing the shear rate after a fine morphology is obtained at higher shear rate. Time resolved SEM performance indicates that, because of the smaller capillary number, particles of the minor phase are almost spherical during the whole coalescence process. An original sizing method based on SEM is used to describe the time evolution of particle size and their distribution. Initially, the volume-average particle size increases rapidly and levels off before a steady state is obtained, while the number-average particle size increases slowly but monotonously during the whole coalescence process. This two-step increase in volume average particle size is discussed in terms of coalescence efficiency. Further, an examination of scaling behavior shows that a master curve for particle growth with different compositions is observed by plotting the relative increase in particles size versus the shear strain, confirming that the evolution of particle size could be described by a scaling law. (c) 2007 Wiley Periodicals, Inc.