Twenty-two 5-week-old male Wistar rats fed an n-3 fatty acid-adequate diet were supplemented with docosahexaenoic acid (DHA) administered perorally for 14 weeks. Six weeks after the start of the administralion, the rats were for 5 weeks trained to acquire a reward at the end of each of 4 arms of an 8-arm radial maze. The retention test interposed with a delayed task (20-min interval after acquiring the first 2 rewards) was then given to each rat to determine spatial working memory retention DHA administration reduced the number of working memory errors after the 20-min interval in the retention test and tended to induce an increase in the DHA/arachidonic acid ratio in the hippocampus, indicating that chronic administration of DHA to rats fed an n-3 fatty acid-adequate diet is conducive to the improvement of working memory-related learning abiiity.