Turkish President Abdullah Gul has signed into law constitutional amendments which allow women to wear Islamic headscarves at universities.
The headscarf issue provokes strong reactions on both sides
The main opposition party in Turkey, where the state is strictly secular, has said it will ask the Constitutional Court to quash the law.
Correspondents say Turkey's secular elite fear the reform will undermine the separation of state and religion.
Parliament passed the amendments by an overwhelming majority a few weeks ago.
One states that everyone has the right to equal treatment from state institutions and the other that "no-one can be deprived of [his or her] right to higher education".
Mr Gul "did not find the amendments in contradiction with the general principles of law, the basic tenets of the republic and procedural rules governing constitutional amendments", a statement said on Friday.
A strict headscarf ban had been in force in Turkish universities since 1997. The ban came after the staunchly secularist military exerted pressure to oust a government it saw as too Islamist.
The changes state that only traditional scarves will be permitted in universities, tied loosely under the chin.
Headscarves that cover the neck are still banned, as is the chador and the all-enveloping burka.