The measure is titled the Daniel Pearl Freedom of the Press Act after a reporter for The Wall Street Journal who was killed by Pakistani terrorists in 2002.
In a signing ceremony at the White House attended by Pearl's family, Obama said the legislation "sends a strong signal about our core values when it comes to the freedom of the press."
"All around the world there are enormously courageous journalists and bloggers who, at great risk to themselves, are trying to shine a light on the critical issues that the people of their country face; who are the front lines against tyranny and oppression. And obviously the loss of Daniel Pearl was one of those moments that captured the world's imagination because it reminded us of how valuable a free press is, and it reminded us that there are those who would go to any length in order to silence journalists around the world."
Obama said the State Department list will single out countries where press freedoms are withheld and "subjects them to the gaze of world opinion in ways that I think are extraordinarily important."