The effect of benzyladenine (BA) on lipid peroxidation and compositions of total insoluble proteins and chloroplast thylakoid protein from wheat primary leaves during senescence in the dark was studied. BA ($10^{-5};M$) treatment prevented conspicuously the loss of chlorophyll content and soluble and insoluble leaf protein contents in senescing wheat leaf segments during 4-day dark incubation. Under the BA treatment, especially, the level of insoluble protein was highly maintained than that of soluble protein. Also, the increase of malondialdehyde (MDA: the peroxidation product of membrane lipids) content was inhibited in the BA treated leaves. Three major polypeptide bands in quantity corresponding to 57, 26 and 12 KD molecular weight were clearly resolved with other minor bands by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) in the insoluble protein fraction. The insoluble protein profiles of the control leaves showed a remarkable decrease in the intensity of the 57 and 12 KD band except for 26 KD band in the 72 h dark incubation. This loss during dark incubation was reduced by BA treatment. More than 20 polypeptides were resolved in the chloroplast thylakoid membrane fraction with the most prominent bands which are 59 and 57 KD ($alpha;and;eta$ subunit of coupling factor: CF) and 26 KD (apoprotein of LHCP). The changes in thylakoid protein profile during 72 h dark incubation showed the rapid degradation in control, but this degradation was prevented in quantity by BA treatment. The above results suggested that BA would inhibit the peroxidation of membrane lipids, thereby preventing the loss of membrane proteins which led to the maintenance of the membrane integrity including chloroplast thylakoid.lakoid.