A series of porous phosphate heterostructure (PPH) samples with different content of silica intercalate were prepared and characterized by XRD, N-2 adsorption and SEM. The total and accessible surface acidity of these samples were measured by NH3 and 2,6-di-tert-butyl-pyridine-TPD, respectively. Not the total acid sites but the accessible ones play a crucial role in the alpha-pinene isomerization reaction. The number of the accessible aid sites is strongly depended on the porosity of PPH samples. 68.1% conversion of alpha-pinene with 51.9% yield of useful products is achieved at 110 degrees C.