Polyacrylic acid (PAA) and polyvinyl alcohol (PVA) are well-known FDA-approved biocompatible polymers. A novel method for preparing PAA/PVA complex nanoneedles in PVA aqueous solution is presented in this article. The PAA/PVA complex nanogels are obtained via polymerization of acrylic acid monomer after PVA nanoparticles formed in water/acetone cosolvent. The results of TEM images showed that the PVA chains were aggregated to form gel particles with some erose nanoparticles. As AA monomers polymerized around PVA nanoparticles, PAA/PVA complex nanogels formed. The PAA/PVA nanogels had an average diameter of 300-100 nm with AA concentration of 0.5-2 g/100 mL. As acetone concentration varied, TEM images demonstrated that the morphologies of resulting nanogels are different. Without acetone in PVA aqueous solution, however, PAA/PVA complexes aggregated to form earthnut-like particles. These results show that the shape and size of PVA/PAA nanogels can be tailored as a template or core for the formation of PAA/PVA nanogels. These PAA/PVA nanogels exhibited pH-induced phase transition due to protonation of PAA chains. The novel PVA/PAA nanogels promise to be developed into pH-controlled drug delivery system. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 358362, 2009