3,3,4,4,5,5-hexafluorocyclopentene (6FE), 1,3,3,4,4,5,5-heptafluorocyclopentene (7FE) and octafluorocyclopentene (8FE) are considered as new generation of potential chlorofluorocarbons substitutes. To investigate the thermostabilities, tubular furnace experiments were designed over temperature range of 500-850℃. The results show that 6FE, 7FE and 8FE are all stable below 650 ℃, thus have good stabilities