The functioning of Vibrio fischeri NAD(P)H: FMN-oxidoreductase (Red) under conditions of macromolecular crowding (MMC) modeled in vitro by adding biopolymers (starch and gelatin) was studied. The dissociation rate constants and the activation energies of dissociation of Red to the subunits were calculated; the process of denaturation of Red was analyzed. It was shown that the functioning of Red both under conditions of MMC and diluted solutions is the same. The result refutes the common belief that due to MMC the stabilization of enzymes’ native conformation occurs in vivo when compared to in vitro.