The Kurdistan Workers Party, or PKK, announced in May it would disband and renounce armed conflict, ending four decades of hostilities.
The move came after PKK leader Abdullah Ocalan, who has been imprisoned on an island near Istanbul since 1999, urged his group in February to convene a congress and formally disband and disarm.
The ceremony took place on Friday in the mountains outside the city of Sulaymaniyah in northern Iraq's semi-autonomous Kurdish region.
The state-run Iraqi News Agency reported that "the process will take place in stages, with a group of party members initially laying down their weapons symbolically".
The disarmament process is expected to be completed by September, the agency reported.
The PKK has long maintained bases in the mountains of northern Iraq. Turkish forces have launched offensives and air strikes against the PKK in Iraq and have set up bases in the area.
Scores of villages have emptied as a result.
The Iraqi government in Baghdad last year announced an official ban on the separatist group, which has long been prohibited in Turkey.
It was not immediately clear how many fighters took part in Friday's ceremony.
Officials had earlier said that the number might be a few dozen.
