The immobilisation of biological matter plays an important part in creating biologically active systems for applications preferably in biotechnological processes or in medical treatments. The immobilisation by polyelectrolyte complex formation, allowing the encapsulation of sensitive biological objects or materials without causing any damage to them, has become a powerful alternative method. In more detail experimental results on capsule formation with sodium cellulose sulphate and poly(diallyldimethylammonium chloride) as reaction compounds are reported. Capsule formation and capsule properties (morphological features, cut-off, rate of NaCS conversion, size and mechanical stability) are looked at under polymerchemical and physicochemical aspects. The importance of osmotic effects is revealed. It is shown that the capsule properties depend not only on the chemical structure of the polyelectrolytes or the conditions of capsule preparation, but also remarkably on the polymerchemical characteristics of the reaction components, particularly on their molecular mass and/or molecular mass distribution.