A study by the technique of electron spin resonance (ESR) has been made on the interaction between the liposomes containing unsaturated fatty acid and cancer cell membrane, and probed into that they have may be biological significance in damaged and inhibited cancer cells. Experimental results showed following: the effect of the oleic heterogeneous liposomes causes that the powerful fixed effect of the spin probe is weakened that the weak fixed effect of the spin probe is strengthened, and that the free direction of the spin probe movement is increased. The effect of linoleic heterogeneous liposomes causes that the powerful fixed effect of the spin probe is strengthened, and the weak fixed effect of the spin probe was weakened on the membrane of mammary tumor, and that the free direction of the spin probe movement is impeded. The effect of ricinoleic heterogeneous liposomes is the same with linoleic heterogeneous liposomes on the neoplasm cell. The result indicates that the unsaturated fatty acid can react with mercaptan groups and change the conformations of membrane proteins of tumor cells.