There are hundreds and thousands kinds of biomacromolecules within cells, proteins, nucleic acids, polysaccharides and so on, and the total concentration of those macromolecules could be high up to 80～200 g/L. In general, cellular interiors are 20%～30% volume-occupied physically by macromolecules, and such an intracellular environment has been termed as “macromolecular crowding” or “the excluded volume effect” more precisely. The biophysical theory has predicted significant effects of macromolecular crowding on biochemical reactions thermodynamically and kinetically, however, the important aspect of the intracellular environment is largely neglected. It has been strongly suggested that addition of crowding agents at biologically relevant concentrations to working system should become a routine variable just like pH and ionic strength to make the study under more physiologically relevant conditions.