Creep properties at 800 C are investigated for a newly developed solid oxide fuel cell BaO-B2O3-Al2O 3-SiO2 glass-ceramic sealant (GC-9) in variously aged conditions using a ring-on-ring test technique. GC-9 specimens are thermally aged at 750 C for 4 h (designated as non-aged), 100 h, or 1000 h after sintering at 850 C. Results show a longer thermal aging treatment leads to a higher crystallinity and greater creep resistance for the given glass-ceramic sealant. When subjected to an applied constant load at 800 C, the 1000 h-aged GC-9 lasts much longer than the non-aged and 100 h-aged ones before rupture. The 1000 h-aged GC-9 also exhibits a creep strain rate much smaller than that in the non-aged and 100 h-aged samples. The value of creep stress exponent increases from 6 to 29 as the aging treatment time is increased from 4 h to 1000 h. The creep strength at a rupture time of 1000 h for the non-aged, 100 h-aged, and 1000 h-aged GC-9 is about 21%, 28%, and 39%, respectively, of the corresponding Weibull characteristic strength at 800 C.