The law granting the official status was the focus of intense opposition, RIA Novosti reported.
Authors of the bill contend that it preserves Ukrainian as the only state language.
Governments and executive bodies can now publish officials documents in Russian and television stations can broadcast in Russian.
The country's legislature, the Supreme Rada, passed the bill July 3 and President Viktor Yanukovych signed it Wednesday.
Ukrainian, predominantly spoken in the western regions of the country, is the only official language. Roughly half the country claims to be Russian-speaking, and a movement has begun to protect the rights of Russian speakers.
Critics charge the bill was rushed through the Rada to please the president's support base. Opposition groups said Thursday they will hold protests in regional capitals to prevent implementation of the law.