They urged the Turkish parliament to rescind the authorisation that it gave to the government to carry out cross-border raids against the PKK, saying the fighters in turn should refrain from hostilities.
Emine Ayla, one protester and member of parliament, told the crowd from the top of a bus: "We don't need another 30 years or another 30,000 deaths to understand that the policy of violence doesn't solve the Kurdish problem."
Ayla also called for an improvement in the "living and health conditions" of Abdullah Ocalan, the founder of the PKK who is serving a life sentence.
In defiance of Turkish law, some people in the crowd held posters that showed Ocalan's image.
Ocalan's welfare is a concern for DSP party members, reflecting the sway that the imprisoned leader holds over many Kurds.
The DSP party won 20 seats in the 550-seat legislature in last year's general elections, leading to hopes that the many disaffected Kurds in Turkey were poised to play a meaningful political role.
But the mood has soured since then, with prosecutors seeking to close down the party because of reported subversive activity.
On Wednesday, the leader of the party, Nurettin Demirtas, went on trial on charges that he used forged health documents to avoid military service.
Demirtas, who was jailed for 10 years for PKK membership and denies the current charges, faces up to five years in prison.
Most Turkish men must serve in the army for up to 15 months, and many do their service in zones where Kurdish fighters are active.
In related news, two police officers were wounded in a bomb explosion in Turkey's mainly Kurdish southeast, the Anatolia news agency reported on Wednesday.
A roadside bomb was set off by remote control as a police vehicle was driving past late on Tuesday in the town of Yuksekova, in Hakkari province bordering both Iraq and Iran, the report said.
One of the officers in the car sustained serious injuries.
No group immediately claimed carrying out the attack, but the PKK is active in the region.
The PKK, listed as a terrorist group by Turkey, has threatened retaliation following Turkish air raids on its bases in northern Iraq.
Since December 16, the Turkish army says it has carried out five air raids against PKK positions in northern Iraq as well as a ground operation to stop a group of fighters trying to enter Turkey.
The PKK has been fighting for Kurdish self-rule in Turkey's southeast and east since 1984 in a conflict that has claimed more than 37,000 lives.