The declaration by the Kurdistan Workers Party (PKK) on Friday comes after a spate of recent violence in which at least 20 people have died.
"The ceasefire will end on 1 June," said a statement from the PKK leadership, based in northern Iraq.
"The ceasefire's political and military meaning has been lost with the Turkish state's destructive operations over the last three months," said the statement, carried by the Europe-based Mezopotamya agency, a mouthpiece for the rebels.
"(The PKK) is warning foreign investors and tourists that with the end of the ceasefire, Turkey has become a risky country for economic investment and tourism," the statement said.
The PKK took up arms against Turkey in 1984 in a bloody campaign to carve out an ethnic homeland in the country's mainly Kurdish southeast.
More than 30,000 people, mainly Kurds, died in the conflict, but the violence fell off sharply with the 1999 capture and imprisonment of PKK commander Abdullah Ocalan.
A resurgence in violence could inflame tensions with neighbouring Iraq, where most PKK fighters are based.
Washington has urged Turkey not to intervene next door as US forces struggle to stabilise the Arab country.
The EU has often criticised the
treatment of Kurds in Turkey
It could also complicate relations with the European Union, which Turkey wants to join. EU members were critical of Turkey's treatment of Kurds in the 1980s and 1990s, accusing Turkish authorities of torture and other abuses.
The PKK threatened to end its unilateral ceasefire, announced in 1998, as recently as last September, then extended its truce.
Turkey has always refused to negotiate with the guerrillas, rejecting the ceasefire as a ruse.
This month has been the southeast's bloodiest in years, with at least 12 PKK fighters and eight security personnel killed.
A PKK fighter was killed on Friday in the remote mountains of Sirnak province, which borders Iraq, after a gun battle with security forces, a security official said.
In the southern city of Adana, which has been spared much of the violence seen in the southeast, police exchanged fire on Friday with three suspected PKK members, wounding two of them, Cihan news agency said.
Ankara has accused its close NATO ally the United States of not doing enough to stamp out the PKK's strongholds in northern Iraq.
Turkey keeps thousands of soldiers along the northern Iraqi border to pursue some 5000 rebels in mountain camps there.