SUP and Six Apart first partnered in October 2006 to launch the Russian version of LiveJournal, which accounts for 28 percent of LiveJournal's audience.
It's the second time LiveJournal has changed hands: In 2005, Six Apart purchased it from founder Brad Fitzpatrick. Six Apart said that during its stewardship of the site the number of accounts grew from 5 million to 14 million.
Six Apart will continue to represent LiveJournal for advertising and sponsorship for at least the next 12 months, the company said.
In future, Six Apart will focus on core products Moveable Type, Vox, and TypePad, it said. On Sunday, the company announced it is hiring staff to work at TypePad.
It will also continue investing in open source platform technologies such as Memcached, Mogile, Perlbal and OpenID, developed by LiveJournal and now used by other sites including Craigslist and Facebook.