Arthur O. Sulzberger Jr., chairman of The New York Times Company, sold 50,000 shares of his company’s stock last week, a day after declaring that the family-owned newspaper was not for sale.

According to a Securities and Exchange Commission filing released on Monday evening, Mr. Sulzberger sold 50,000 shares at $12 a share on Aug. 8. The filing noted that Mr. Sulzberger continued to own 173,675 Class A shares in company stock.

Eileen Murphy, a spokeswoman for The New York Times Company, said that the stock sale “is part of Arthur’s normal estate planning.”