The present investigation describes the preparation and characterization of novel biodegradable nanoparticles based on complexation of polygarnma-glutamic acid (gamma-PGA) with bivalent lead ion. The prepared nano-systems were stable in aqueous media at low pH, neutral and mild alkaline conditions. The particle size and the size of the complexes were identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that the size of the complexes depended on the pH and concentrations of gamma-PGA and lead ions. Particle sizes measured by TEM revealed that at low concentrations, nanosized particles were formed, however, at high concentrations of gamma-PGA and lead ions, the formation of large aggregates with a broad size distribution was promoted. The size of individual particles was in the range of 40-100 nm measured by TEM. The results from the DLS measurements showed that the low and high pH values in mixtures with high concentrations of gamma-PGA and Pb2+ ions favored the growth of large complexes. The gamma-PGA nanoparticles, composed of a biodegradable biomaterial with high flocculating and heavy metal binding activity, may be useful for various water treatment applications. (C) 2007 Elsevier B.V. All rights reserved.