Sulzberger sold 50,000 Class A shares on Thursday for $600,000, or $12 each, according to a U.S. Securities and Exchange Commission filing on Monday. The stock closed at $12.04 on Monday.

A New York Times spokeswoman said the sale was part of Sulzberger's normal estate-planning and represented a very small percentage of his stake, which includes stock options and Class B shares that vote on 70 percent of the board.

The Ochs-Sulzberger family controls the New York Times through a trust of Class B shares.

Sulzberger sold his shares days after Amazon.com Inc founder Jeff Bezos bought The Washington Post for $250 million, stunning media watchers. The Grahams, who control The Washington Post Co, are one of the last families whose ownership of newspapers spanned generations.

The deal prompted Sulzberger to issue a memo to New York Times staff to address the question if the Ochs-Sulzbergers, who have been without a dividend since 2009, would be the next family to exit the business.

"Will our family seek to sell the Times?" Sulzberger wrote according to the New York Times. "The answer to that is no."

Newspapers are facing unprecedented challenges because of dwindling advertising dollars and readers who choose to get their news on smartphones and tablets.

In recent months several newspapers have gone on the block or changed hands. The New York Times sold The Boston Globe to Boston Red Sox and hedge fund owner Jack Henry for $70 million. The Tribune Co, which publishes the Los Angeles Times and the Chicago Tribune, is exploring a sale of its newspaper group and said it would separate its publishing assets from its broadcast division.

(Reporting by Jennifer Saba in New York; Editing by Lisa Von Ahn)