Lipid membrane has a significant role to retain waters on its surface due to high hydrophilicity of head groups of lipid molecules. Although many physical chemical properties such as thickness, phase state, fluidity etc. can be measured by the recent experimental equipments, the water retaining capacity of membrane is still difficult to be analyzed. Molecular dynamics simulation was performed to theoretically estimate the retaining time of waters on membrane surface. Different kinds of lipid bilayers were modeled using sphingomyelin molecules, which is one of the typical components of biomembrane. Our simulation successfully generated the stable and equilibrated bilayer structures of sphingomyelin with different carbon chain length. Thickness, area per lipid, order parameter, and gauche ratio were deduced from the simulation data. In this work, we propose a technique to estimate the distribution function of waters on membrane surface, which enables us to evaluate the water retaining time on membrane. Our calculation technique will be helpful for design an artificial membrane whose moisture property is controlled. [DOI: 10.1380/ejssnt.2009.591]