The 400-page manuscript turned up earlier this month at the Samuel T. Freeman & Co. auction house in Philadelphia when the daughter of one of the author's former secretaries tried to put it up for auction. Officials there notified investigators, federal authorities said Wednesday.
The original typed manuscript, complete with Buck's handwritten edits, went missing from her family farm in suburban Philadelphia around 1966. The author long believed it had been stolen.
While it appears the manuscript may have been "inappropriately obtained," no charges would be filed, U.S. Attorney Patrick Meehan said.
"To the extent that somebody may have been suspicious some number of years ago, that was some number of years ago," Meehan said. He declined to identify the person believed to have taken the manuscript, but said she had worked as a secretary for Buck.
Federal authorities said the manuscript could be worth at least$150,000 (111,624 EUR), but officials at the auction house said there is really no way to know the actual value.
The manuscript is in FBI possession for now, while the family trust and the Pearl S. Buck Foundation decide what to do with it.
Buck died in Vermont in 1973, having long wondered what happened to the original version of one of her most renowned works.
The 1931 novel, centered on village life in rural China, helped earn Buck the Nobel Prize for Literature in 1938, making her the first American woman to win the honor. The novel won the Pulitzer Prize in 1932.
The pages were found in excellent condition in a suitcase, along with a collection of letters from people including Eleanor Roosevelt and Harry Truman. Authorities did not say where they had been kept, but said the secretary's family had taken them for consignment at the auction house.
"It appears they have been in the possession of this woman's family for some period of time," Meehan said.
Buck, the child of Presbyterian missionaries, spent much of the first half of her life in China. But she was once denied a visa on the grounds that her writings showed an "attitude of distortion, smear and vilification towards the people of new China."
After receiving the manuscript earlier this month, the auction house faxed a copy of one page to the Pearl S. Buck Foundation in an attempt to verify its authenticity, said Joe Huenke, an assistant in Freeman's rare books department.
Using Buck's old typewriter, the foundation determined the manuscript to be authentic. But officials there also told the auction house it had been reported stolen long ago.
"As soon as we learned that it was reported stolen, we really had no choice but to alert the authorities," Huenke said.