The structural transformation of VPI-5 to AlPO 4 -8 has been investigated by temperature-dependent photoacoustic (PA) measurements. The observed enhancements of the PA signal intensity for the VPI-5 samples evacuated below 473 K are considered to be due to the periodic evaporation of adsorbed water molecules from the sample surfaces. The sharp decreases in the PA signal during a temperature raise from room temperature to ca. 438 and 463 K are attributed to Al-O-P bond breakage. These decreases can be considered as a measure of the structural transformation of VPI-5 to AlPO 4 -8. Two endothermal processes, namely dehydration and bond breakage during structural phase transition, can be observed separately by means of the temperature-dependent PA technique.