The envelope, inscribed in black brushstrokes 'To Mr Fu Yisheng and Mr Bo Yibo' by Mao, sold for 6.55 million yuan (USD 1.08 million) yesterday, the China Guardian auction house said on its website.
The document contained in the envelope was not included, in compliance with government regulations against selling leaders' letters.
Bo was a high-ranking revolutionary general who fought both the Nationalists and Japanese before being jailed and tortured in the 1960s during Mao's Cultural Revolution.
"The envelope was issued by the People's Revolutionary Military Committee of the Central People's Government. It is rare and preserved well," China Guardian said in a description.
The committee existed in the early years of the People's Republic, which was founded in 1949, and preceded what is now China's Central Military Commission.
Bo Xilai was sentenced to life in jail for corruption in September.
