Polyprenols have been found in many bacterial and plant membrane fractions. Long-chain polyprenols with 12-100 isoprene residues have been isolated from the green leaves of Spermatophtyta. The pattern of polyprenols is species-specific. Polyprenyl phosphates are obligatory intermediates in the biosynthesis of sugar polymers and formation of glycoproteins. Model membranes (BLM and liposomes) made from phospholipid and polyprenols with different number of isoprene residues were investigated in the present study. The electrical (the membrane breakdown voltage and the membrane capacitance) and mechanical properties (the membrane hydrophobic thickness and membrane Young's modulus) of model membranes were measured by the voltammetric technique. The vesicle morphology was analysed by TEM. Polyprenols change studied parameters of membranes appear to increase the fluidity of phospholipid bilayers and destabilize membranes. This effect depends on the number of isoprene units in the polyprenol molecule. The micrographs show that lipid vesicles prepared from PC are regular whereas lipid vesicles prepared from prenol/phospholipid, besides regular structures, form several irregular characteristic structures. The results can be regarded as the evidence that lipids, may directly influence the activity of biological membranes by changing their fluid-crystalline properties. Some functions of polyprenols in bilayers are connected with modification of some properties of the membranes.