The Hugoniot equation-of-state (EOS) of porous iron with an average initial density of 6.904 g/cm³ has been measured in the pressure range from 90 to 160 GPa, and a good straight fitting D = 2.997 + 1.603 u has accordingly been obtained, where D is the shock wave velocity and u the particle velocity, both in units of km/s. Combining this with the Hugoniot EOS of non-porous iron, the Grüneisen EOS and the Rankine-Hugoniot energy conservation relation, and taking the possible solid-liquid transition correction, we have calculated the Grüneisen parameter γ of iron and obtained the result γ₀ρ₀ = γρ = const, with γ₀ = 1.945 and ρ₀ = 7.856 g/cm³, ρ being the density. PACS:  62. 50. +p, 65. 90. +i, 91. 35. -x