Turkey's block on access to Twitter violated freedom of expression and individual rights, the country's constitutional court has said.
It is the most significant legal challenge yet to a ban which caused public uproar and international condemnation.
Turkey's telecoms authority (TIB) blocked access to Twitter on 21 March after Prime Minister Tayyip Erdogan said he would "root out" the network.
His comments came following a stream of anonymously posted audio tapes purporting to expose corruption in his inner circle days ahead of nationwide elections.
The constitutional court said it had sent its verdict to the TIB and the Transport Ministry, which also has responsibility for communications. It was not immediately clear whether the ruling would lead to a lifting of the block.