Porous hydroxyapatite (HAp) as a bone graft substitute was produced via gas technique with three different concentrations of hydrogen peroxide (H2O2) namely 20, 30 and 50%. Hydroxyapatite(HA) slurries with different concentration were produced by mixing between H2O2 solutions and HA powder (L/P) with different ratio i.e. 0.9 to 2.20 ml.g-1. Different L/P ratio and H2O2 concentration affected the porosity, interconnectivity and compressive strength of HAp sample. Changes in L/P ratio between 0.9 to 2.20 ml.g-1, increases the porosity around 50 - 65% at 20% H2O2 concentration. Porosity increases with the L/P values and H2O2 concentration which 76% of porosity was obtained at 50% H2O2 and 2.20 mlg-1 of L/P. The compressive strength of HAp is in the range of 0.5 to 2.15 MPa and is found decreasing with the increasing of L/P values.