Dieter von Holtzbrinck, an heir to a German publishing empire, resigned from Dow Jones & Co.'s board of directors to protest the board's decision to endorse a $5 billion offer from News Corp.

"Although I'm convinced that News Corp. offer is very generous in financial terms," he wrote in a letter to directors Thursday, "I'm very worried that Dow Jones unique journalistic values will long-term strongly suffer after the proposed sale."

Mr....