In this work, we study the preparation and pervaporation application of thermally cyclodehydrated poly(imideoxadiazole) (PIO) membranes. The poly(imide-hydrazide) (PIH) precursor is firstly fabricated by the crosslinking of polyimide by 1,3,5-benzenetricarboxylic acid trihydrazide (BTCH). Then a thermal treatment is applied to induce the cyclodehydration of PIH into PIO. The effects of thermal treatment temperature on membrane properties and the pervaporation performance for isopropanol dehydration are investigated and characterized by various techniques. The results show that the thermal treatment has two opposite effects, i.e., thermal annealing and thermal cyclodehydration, which are both enhanced with the increase in the thermal treatment temperature. When a low thermal treatment temperature is applied (200-275 degrees C), the thermal cyclodehydration plays the leading role, resulting in the impressive increase of the flux with reasonable separation factor. While for PIO membrane treated with a relative high thermal treatment temperature (> 300 degrees C), the physical annealing may play the dominant role and leads to an opposite effect. Thus, with a suitable thermal treatment temperature (300 degrees C in this study), an optimized separation performance of the cyclodehydrated PIO membrane could be achieved. In addition, the effect of the operation temperature on the membrane performance and the long-term stability are also studied. The obtained promising performance indicates a great potential of the developed PIO membranes for pervaporation or other membrane-based separation applications.