Reversible pH-induced swelling of (PAH/PSS) polyelectrolyte microcapsules is accompanied by increase porosity, making them permeable to poly(acrylic acid)(PAA) at pH values higher than 11.2. This pH-switchable permeability was used to encapsulate the polyanion in alkaline conditions. Relationship between starting PAA concentration in solution and amount finally being encapsulated has been established and can be used further as calibration curve. A desired amount of encapsulate polymer in the picogram range per capsule can be achieved. The loaded capsules were then used as microreactors by forming a complex between the PAA and Ca2+ ions.