In this work, growth of lightly crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) brushes and subsequent capsule formation using Pickering emulsion interface-initiated atom transfer radical polymerization (PEII-ATRP) were investigated. Initiator-immobilized silica nanoparticles (2.5 initiators/nm(2)) assembled at the interface of paraffin oil-in-water emulsions and ultimately stable Pickering emulsions were formed. PEII-ATRP was conducted in the water phase of Pickering emulsions from the part of the surfaces of initiator-immobilized silica nanoparticles exposed to water by using copper(l) chloride/bipyridine as catalyst at 35 degrees C. As PHEMA has a character of lightly crosslinking when the polymerization occurs in water, novel hybrid capsules ("colloidosomes") can be obtained and were observed by confocal laser scanning microscope (CLSM) and optical microscopy (OM). The semipermeability of the resultant hollow capsules was demonstrated by the diffusion of 1-phenylazo-2-naphthol. Meanwhile, the conformation of PHEMA chains can be varied in different solvents, which affects the semipermeability of these hybrid hollow capsules. We expect these hollow capsules can be further utilized to develop microdevices for drugs or cells delivery. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1354-1367, 2009