Reagan, 86, was taken to St. John's Health Center, where doctors determined she did not break a hip as feared when she fell early Sunday, her spokeswoman Joanne Drake said.
She underwent more tests on Monday.
"I am pleased to report that doctors have concluded their tests, all results are good and they intend to release Mrs. Reagan from the hospital tomorrow," Drake said in a statement Monday night.
Reagan spent the night in the same room where former President Ronald Reagan stayed after he broke his hip at home in 2001. He died June 5, 2004, after a 10-year battle with Alzheimer's disease.
The two were married for 52 years.
Nancy Reagan's last major public appearance was at the Jan. 30 Republican presidential debate at the Reagan Library in Simi Valley, Calif., where she sat with Gov. Arnold Schwarzenegger.
She did not attend a 97th birthday celebration held for her late husband at the library on Feb. 6.
