In this paper, two kinds of nanoporous Mg are prepared by a physical vapor deposition method, and their hydrogen generation properties are investigated based on the hydrolysis reaction with salt water. The results indicate that cell-like nanoporous Mg has higher hydrogen generation amount of 800 ml g(-1) and hydrogen generation rate of 48.1 ml g(-1) min(-1) than block-like nanoporous Mg, while block-like nanoporous Mg with the substrate shows better hydrogen generation property of 933 ml g(-1) and 78.4 ml g(-1) min(-1). The effects of concentration of salt water and temperature on their hydrogen generation property have been investigated. In order to explain their excellent hydrogen generation properties, electrode potential and specific surface area of different Mg materials are examined. The results indicate that cell-like nanoporous Mg has a more negative potential (-2.410 V (vs.RHE)) than block-like nanoporous Mg (-2.279 V (vs.RHE)), and a higher specific surface area of 26.7 m(2) g(-1) than block-like nanoporous Mg of 0.9 m(2) g(-1), both of which are more negative and higher than that of Mg plate and Mg alloy plate. Thus, it can be concluded that more negative potential and higher specific surface area of nanoporous Mg are the reasons for their better hydrogen generation property.