The effect of docosahexaenoic acid (DHA) on maze-learning ability in aged mice was investigated. Aged mice fed a diet deficient in n-3 fatty acid received a semi-purified diet of 0.5, 1 and 2% DHA-ethyl ester (DHA-EE) for 4 months. Maze-learning ability was assessed at 3 months after the start of the experiment. The time required to reach the maze exit and the number of times that a mouse strayed into blind alleys in the maze were measured in 3 trials conducted at 4-day intervals. The time was significantly less in the DHA-EE 0.5% and DHA-EE 2% groups than in the control group (p<0.05). The number of times mice strayed into blind alleys in the maze was significantly lower in the DHA-EE 2% group than in the control group (p<0.05). Mice fed DHA showed increased DHA and decreased level of arachidonic acid (AA) in the brain. These results suggest that the intake of a 2% DHA diet improves learning ability in aged mice, which is associated with a higher DHA content in the brain.