Polypropylenimine dendrimer (DAB-Am-32, generation 4.0) was converted into a macroinitiator DAB-Am-32-Cl via reaction with 2-chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH2)(32)-polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB-Am-32-Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, H-1 NMR, and C-13 NMR. The structure of poly(propylene imine)(NH2)(32)-polystyrene was characterized by FTIR spectrum and H-1 NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH2)(32)-polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30-80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB-Am-32-0, the number-average diameter (D-n), weight-average diameter (D-w) were both increased gradually. With enhancing the surfactant concentration, the measured D-h, of the nanoparticles decreased, while the polydispersity increased. (c) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892-2904, 2009