Tumblr recently joined
the list of foreign sites — including Facebook, Google, Medium, Twitter, and Wikipedia that are blocked in China.
Tumblr has been blocked in China since May 29, according to tests done by GreatFire.org
While the reason for the sudden block is unclear, there’s speculation that it’s because of the amount of porn that exists on the Yahoo-owned property.
As of now, Reddit is the only foreign social network that stays unblocked
by The Great Firewall of China.