In this work, the porous Magnesium alloy (AZ91 ) was prepared by Space holder technique to deposit carbon nanotubes, Novalac powder was used as space holding and fugitive materials with different particle size (≥20 µm, ≥500 µm) and amount (50, 52, 54, 56, 58, 60%wt.). Impact of Novalac powder (particle size and additive percent) on density and porosity of porous AZ91 alloy was studied. Fine Novalac powder (≥20 µm) not recommended in the porous AZ91 alloy preparation, concurrently coarse Novalac powder (≥500 µm) was suitable for that purpose. It was found that the density of AZ91 alloy decreased with increasing Novalac concentration. Carbon nanotubes were deposited on the porous AZ91 alloy by catalytic chemical vapor deposition whereas NiSO4.6H2O used as catalyst, acetylene gas as a carbon source and argon gas as a carrier gas with flow rate percent 1:1, at 575°C process temperature for 30 min. Multiwall carbon nanotubes were obtained and characterized by X-ray diffraction and scanning electron microscopy techniques. The average diameter of the multi wall carbon nanotubes was (46 nm). Although the porosity percent of AZ91 alloy was not majorly effect proportionally by the increasing of an additive Novalac percent, the yield (quantity) of Multiwall carbon nanotubes was enhancing due to increase the porous AZ91 alloy surface area.