Three porous metals, i.e., lotus-type porous copper, aluminum foam, and open-cell type porous nickel, were subjected to multi-pass cold rolling. At the beginning, thickness reduction was mostly converted to volumetric change, while after heavy rolling, elongation in the rolling direction became remarkable. It is found that strain ratio of elongation to thickness, i.e., 'elongation efficiency', increases with decreasing porosity. The trend is sensitive to neither initial porosity nor pore morphology. It can be described with Shima's eq. for sintered metals using modified constants.