A series of porous phosphate heterostructure (PPH) samples with different content of silica intercalate were prepared and characterized by XRD, N2 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 α-pinene isomerization reaction. The number of the accessible aid sites is strongly depended on the porosity of PPH samples. 68.1% conversion of α-pinene with 51.9% yield of useful products is achieved at 110 °C.