The astronauts took off from the Jiuquan Satellite Launch Centre in northern China.
They will dock with the experimental Tiangong 2 space lab and spend 30 days there, the longest stay in space by Chinese astronauts.
This and previous launches are seen as pointers to possible crewed missions to the Moon or Mars.
An earlier Tiangong - or Heavenly Palace - space station was decommissioned earlier this year after docking with three rockets.
