Molecular dynamics simulations of pure DPPC and DPPC/cholesterol bilayers under stretching with various stretching speeds were performed. The lower the stretching speed, the more ordered the DPPC molecules, which tendency was more prominent in the DPPC/cholesterol bilayer. The critical areal strain, where the rupture occurs, in the pure DPPC bilayer significantly increased with the increase of the stretching speed, whereas that in the DPPC/cholesterol bilayer did not. The difference of the process of the molecular orientation changes under stretching might cause the difference of the stretching speed effects on the critical areal strain.