The barotropic phase transitions of an asymmetric phosphatidylcholine, 1-palmitoyl-2-stearoylphosphatidylcholine (PSPC), bilayer membrane were observed by the methods of high-pressure light transmittance and differential scanning calorimetry. The temperature-pressure phase diagram and thermodynamic quantities of the phase transitions were compared with those of three kinds of symmetric phosphatidylcholines. The different transition properties of PSPC bilayer from those of symmetric phosphatidylcholines may be attributable to the enhanced cohesive interaction between acyl chains in the gel state of the bilayer membrane.