Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a natural polyester known for its biocompatibility and biodegradability. The hydrolysis of PHBV nanoparticles (90150 nm) and microparticles (3358 mu m) was investigated. Particles were formulated from preformed polymer(s) by miniemulsification/solvent evaporation technique to obtain nanoparticles or by emulsification/solvent evaporation technique to obtain microparticles. The morphology of the nanoparticles was studied by Field Emission Gun-Scanning Electron Microscopy (FEG-SEM). The kinetics of PHBV degradation was followed by gel permeation chromatography. After storage of PHBV nanoparticles for 25 days at 37 degrees C, the Mn and Mw of PHBV was reduced up to 85 and 80%, respectively. PHBV nanoparticles stored at 4 degrees C presented a much lower molecular weight reduction. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013