The canvas is painted on both sides, with a rare nude, believed to have been painted in 1910, on the back.
The Frankfurt museum plans to restore the work and put it on display for the first time when it reopens in the fall of 2011. It did not give an estimate of the painting's value.
Kirchner is one of the best-known German Expressionist painters along with Ernst Ludwig, Emil Nolde and Wassily Kandinsky. He was also part of a movement known as Die Bruecke, or "The Bridge."
The Associated Press contributed to this report