According to RIA news agency, the text of the law said that the Ukrainian peninsula agreed "to enter into the Russian Federation with the rights of a subject of the Russian Federation."
Russia's lower hour of legislature is now considering annexation of Crimea.
There will be a regionwide referendum on March 16. Crimea comprises 60% ethnic Russians.
The region's parliament stated that the autonomous republic was seceding "as a the result of the unconstitutional coup," which is how Russian President Vladimir Putin has described the ouster of Ukrainian President Viktor Yanukovych and the installation of a pro-EU interim government.