The post office had an even larger loss than expected last year -- $8.5 billion.
The agency said Friday it was in the red for 2010. Earlier estimates had put the loss at $6 billion to $7 billion.
It comes despite elimination of more than 100,000 jobs and other cutbacks over recent years.
The post office has seen a sharp decline in mail because of increased use of the Internet and the recession which cut advertising and other business mail.
For the year that ended Sept. 30, the post office had income of $67.1 billion, down $1 billion from the previous year. Expenses totaled $70 billion, a decline of about $400 million. It also was required to make a $5.5 billion payment for future retiree health benefits.