The House of Councillors passed the bill to rename April 29, the late emperor's birthday, Showa Day, after the title of his reigning era. The new name will come into effect in 2007.
Row with Japan: China tells people to be calm
The bill, proposed by the ruling bloc, cleared the lower house on April 5.
The move is likely to spark opposition from China, which recently witnessed massive protests over Japan's handling of its wartime past.
Emperor Hirohito came to the throne in 1926 and died in 1989. The day was known as the
The legislation will shift Greenery Day to May 4, also a national holiday, sandwiched between Constitution Day on May 3 and Children's Day on May 5.
Slideshow: Asia's Monarchs
The bill was shelved for several years in consideration of reactions at home and abroad. After the World War II, Emperor Hirohito was granted immunity from any responsibility. Yet Japan's post-war constitution deprives the emperors of their power by recognizing them as the nation's symbol rather than the head of state, Xinhua said.
The ruling coalition -- the Liberal Democratic Party and the New Komeito party -- and the main opposition Democratic Party of Japan voted for the bill, while the two other opposition parties --the Japanese Communist Party and Social Democratic Party -- opposed the move.
