Tyson is now looking forward to his fight against Nielson
The San Bernardino County district attorney's office reviewed the case on Friday and conducted a follow-up investigation before reaching a decision.
"It's precisely because of Mr Tyson's reputation for violence and his notoriety and his previous conviction for rape that we really, really looked at this case very careful," said deputy district attorney David Whitney.
Whitney also said it was unlikely charges could be filed in the future.
A 50-year-old woman maintains she was sexually assaulted by Tyson on 16 July at a home he rented while training in the San Bernardino Mountains near Los Angeles.
Tyson, who said he was innocent, has since moved to Phoenix to train for a his September fight with Danish boxer Brian Nielsen in Copenhagen.
"There was never a doubt in my mind that, when the authorities took a hard look at the case, the truth would serve to vindicate me," Tyson said in a written statement.
"Now that this is behind me, I am just looking forward to fighting and regaining the heavyweight championship of the world."