A bilayer composed of branch-chained lipid molecules is generally believed to have high bilayer stability and low ion leakage. To understand how the chain branching affects the bilayer properties on the molecular level, two molecular dynamics simulations of lipid bilayers have been undertaken in the isothermal-isobaric ensemble. The first simulation was carried out on the straight-chained DPPC bilayer, the second on the branch-chained DPhPC. The detailed analyses on the chain conformation revealed that the segmental order of branched chains was lower than that of straight chains. As for the intermolecular packing order in the bilayer plane, however, a relatively neat lipid arrangement was observed for the branch-chained DPhPC bilayer. A significant lowering in the chain mobility was observed as a result of chain branching. The high bilayer stability of the branch-chained DPhPC bilayer would arise from the low chain mobility and the neat lateral arrangement of the lipid in the bilayer.