Since aging is the most important risk factor for dementia, measures to slow the onset of brain aging are an important strategy for preventing dementia. Accumulation of oxidative damage is considered to be a major cause of aging. Catechins in green tea (GTCs) have powerful antioxidative activity. Ingestion of GTCs suppressed oxidative damage, brain atrophy and cognitive decline in aged mice. Age-related cognitive decline was significantly suppressed in mice when middle-aged mice started to drink green tea catechins. Middle-aged people are thus expected to be able to suppress brain aging by ingestion of GTCs. In addition, numerous people are stressed under various conditions. Brain aging was accelerated and lifespan shortened in experimental animals that were chronically and psychosocially stressed. Theanine, an amino acid in green tea, suppressed stress-induced aging. However, the anti-stress effect of theanine is blocked by catechins and caffeine that are main components in green tea. Daily drinking of several cups of green tea is considered to suppress brain aging. In addition, theanine-rich green tea or green tea with a lowered level of caffeine is expected to suppress stress and stress-induced aging.