The `Blind Side` actress has given the huge sum to the American Red Cross on behalf of her family to help the earthquake-stricken country.
The organisation said: "The American Red Cross is extremely grateful for this generous support from SandraBullock and her family. This contribution is vitally important as the Red Cross works to provide critical assistance and essential relief items in this time of urgent need for so many people in Japan."
Though the donation from Sandra - who previously gave $1 million to Doctors Without Borders to assist with helping Haiti following an earthquake in 2010 - is the biggest celebrity contribution to be made public, other stars have been backing the cause.
Lady Gaga has raised over $250,000 by designing a wristband - which is read and white and reads "We pray for Japan" in both English and Japanese - which has been on sale for just $5.
She tweeted: "Monsters: in just 48 hrs you`ve raised a quarter of a million dollars for Japan Relief. It`s important we help. X (sic)"
People can donate to the relief fund via The Red Cross through a variety of methods including the charity`s website, Facebook and iTunes.