General outlines of calculation and management of physical property data in a new bioprocess simulation system, named SIMBIOS, are presented. Calculation of thermodynamic and transport properties for pure substances is carried out by short-cut procedures to be generated by means of rigorous methods at the beginning of the simulation. To obtain mixture properties, special mixing rules are used. In case of nonideal and strongly nonideal mixtures, several activity coefficient models are available to calculate phase equilibria and excess properties. Internal, communication facilities inside the system are shown too.