Historical opinion is divided as to whether the emperor was responsible for Japan's aggression before and during the first world war, or whether he was the puppet of military and political leaders.
Hirohito was not tried at the Tokyo war tribunal that sentenced to death seven military and government leaders, including wartime premier Hideki Tojo.
Akihito, who is barred from commenting on politics, said the events during his father's era "taught us many lessons. I believe it is essential for us to learn from the historical facts and prepare ourselves for the future".
No more shrine visits
Many Asian countries still hold bitter memories of Japan's past aggression and have complained that Japan has whitewashed its past in school textbooks.
But Yukio Hatoyama, Japan's centre-left prime minister, who took power in September, has pledged stronger ties with Asia and said he and his cabinet ministers will not visit Tokyo's Yasukuni war shrine.
Akihito's coronation ceremony was held on November 12, 1990, after the end of the mourning period for Hirohito.
Some 50,000 people were expected to gather later for privately organised commemorative events near the moated palace in central Tokyo for traditional and modern music performances.