The aim of this work was to determine the influence of protein content on the physicochemical properties of protein-loaded poly(e-caprolactone) (PCL). To achieve this goal, bovine serum albumin (BSA), an example of protein was encapsulated within PCL matrix by emulsion solvent evaporation method. The polymer matrix's rheological properties, hydrophobicity, molecular weight (M-W), and thermal behavior were determined. Particle characteristics such as BSA loading, surface area, mean size, morphology, and in vitro release profile were also assessed. After encapsulation process, the polymer crystallinity and crystallization point were markedly increased suggesting that a nucleation phenomenon occurred. The increase in PCL M-W (from 46.7 to 179.4 kDa) led to an increase of both particle size and encapsulation efficiency that was consistent with rheological data. The increase of protein content from 1.6 to 11.5% (w/w) influenced considerably particle's specific surface area and decreased the rate of protein release. Together, these results suggest that beside the nature of the carrier polymer, protein content may have implication on their controlled release, the coating of particle by protein, and on the carrier polymer chemistry and degradation. (c) 2006 Wiley Periodicals, Inc.