The diameter, membrane thickness, and compression intensity of hollow Ca-alginate capsules were measured at different gelation conditions, such as the reactant concentration, dropping velocity, and gelation time. The optimum operation conditions for preparing capsules were determined at 100 g/L CaCl2, 10 g/L sodium alginate (Na-alginate), a dropping velocity of 150 droplets/min, and a gelation time of 10 min. Diffusion of some saccharide and amino acid from bulk solution into capsules was investigated, and the diffusion coefficients were calculated by the developed mathematical model. All the tested substances can diffuse easily into the capsules. The combined diffusion coefficients of the capsule D-m are 92-99% as large as their diffusion coefficients in pure water, while the diffusion coefficients in the capsule membrane D-m are 60-95% as large as those. By employing polyethylene glycol (PEG) and bovine serum albumin (fraction V) (BSA(V), the molecular weight cut-off of the capsule was determined. For linear macromolecules, hollow Ca-alginate capsules have a molecular weight cut-off of 4,000. No diffusion of BSA(V) into the capsules was observed. (C) 2004 Wiley Periodicals, Inc.