Michelle Obama told students in China that freedom of speech and unfettered access to information make countries stronger and should be universal rights.
The US first lady was speaking today at Peking University in Beijing during a trip aimed at promoting educational exchanges between the US and China, which has some of the world's tightest restrictions on the Internet.
She said the free flow of information is crucial "because that's how we discover truth, that's how we learn what's really happening in our communities, our country and our world".
Mrs Obama said it makes countries stronger "when the voices and opinions of all their citizens can be heard.
"And that's how we decide which values and ideas we think are best - by questioning and debating them vigorously, by listening to all sides of every argument and by judging for ourselves."
China blocks many foreign news sites and social media services such as Facebook, Twitter and YouTube. Its army of censors routinely filters out information deemed offensive by the government.
Authorities also block some of the country's most outspoken online voices by shutting down their blogs and restricting their ability to register for new accounts.
Earlier this month, China removed dozens of accounts on a popular mobile phone messaging service that had essentially become independent media outlets outside government control.