Murat Karayilan, a senior commander of the armed separatist movement, the Kurdistan Workers Party (PKK), made the announcement on Saturday from the group's base in the remote Qandil Mountains in northern Iraq.
The ceasefire will go into effect on October 1.
Speaking to the press, Karayilan said: "Our fighters would shoot only in the cases where our forces are targeted and we will not carry out any operation of a military nature.
"This ceasefire would be implemented by all parts within the PKK."
The group has not said that it will disarm. However, Karayilan did say that if the Turkish state has a democratic solution for the Kurdish issue the group would consider it.
The ceasefire was also posted on the pro-Kurdish Firat news agency's website. It said the group had heeded a call from Abdullah Ocalan, the imprisoned Kurdish rebel leader.
Ocalan released a statement through his lawyers on Wednesday which called for an unconditional ceasefire.
The decision came 10 days after the Iraqi government said it would shut down all offices belonging to the PKK around the country.
Ali Al-Dabagh, an Iraqi government spokesman, said that the decision was made because Iraq wants to have good relations with Turkey and all neighbouring countries.
Erdogan to meet Bush
Erdogan, the Turkish prime minister, and George Bush, the US president, are expected to meet on Monday in the US to discuss Turkey's battle against Kurdish separatists.
Erdogan has rejected calls
for a ceasefire
Ankara has ignored all previous ceasefires by the group, saying it does not negotiate with terrorists.
Military commanders have vowed to fight until all rebels are killed or surrender.
Erdogan rejected calls for a ceasefire made by Ocalan this week and said that he would accept nothing less than disarmament.
He said in an interview with CNN Turk on Thursday: "Ceasefire is the wrong term.
"The terror group must give up its weapons. Our hope is that they will give up their weapons."
It is believed that up to 30,000 people have been killed in the conflict between the Turkish state and the PKK.