Abstract: Using a modified aging tester to age two types of fluorosilicone oil, FSO-2 and FSO-A, suitable aging test conditions were investigated. Gel chromatography (GPC) was used to analyze the molecular weight of fluorosilicone oil and to observe the changes of oil properties during aging test. Test results showed that when aging temperature was below 250℃, gelation did not occur in these two types of oil; testing under 250—300℃, aging happened in both oils. With prolonging aging time at 300℃, the increase of molecular weight and molecular weight distribution in both oils became significant. It can be seen from the GPC analysis results that the aging mechanisms of these two oils were similar; however, FSO-2 seemed to be more stable and should have a longer service life time.