Abstract: Bleomycin A₆ is one of the compositions of bleomycin, which has selective influence on the membrane fluidity of mouse ascites hepatoma cells and it has no effect in marrow cell and liver cell of normal mouse. Bleomycin A₆ reduces the phase transition point from liquid crystal to liquid state of malignant cell membrane by 2℃. Synergistic effect of the bleomycin A₆ with continual hyperthermia was observed which could cause pronounced changes in the speed of membrane fluidity.