AbstractThe effects of substrate on stabilities of native (NA) and three kinds of immobilized yeast alcohol dehydrogenase (IMA), namely PGA (the carrier; porous glass), SEA (agarose gel) prepared covalently, and AMA (anion‐exchange resin) prepared ionically, were studied. The following results were obtained. (1) The deactivations of NA and IMA free from the substrate or in the presence of ethanol obey the first‐order kinetics, whereas, in the presence of butyraldehyde, their deactivation behaviors are explained on the basis of coexistence of two components of YADHs, namely the liable E1, and the comparatively stable E2, with different first‐order deactivation constants. (2) A few attempts for stabilization of IMA were carried out from the viewpoint of the effects of crosslinkages among the subunits of YADH for PGA and the multibonding between the carrier and enzyme for SEA. The former is effective for the stabilization, whereas the later is not.