To provide a grease composition that is capable of effectively suppressing an early-flaking due to hydrogen embrittlement, and to provide a grease-sealed bearing in which the grease composition is sealed. A grease composition 7 contains a base oil, a thickener, and an additive. The additive contains sodium molybdate as an essential component, and sorbitan-based ester or metal sulfonate. The metal sulfonate is Ca sulfonate or Zn sulfonate. The content of the metal sulfonate is less than 3 parts by mass relative to 100 parts by mass of a total of the base oil and the thickener.