The blast happened in Dera Bugti district of Baluchistan province on Friday.
Raziq Bugti, a provincial government spokesman blamed autonomy-seeking militants for planting the mine.
"Most of the dead are women and children. Seven people were injured," Bugti said.
Baluch militants have waged a low-level insurgency for greater control over gas and other resources for decades, but have intensified attacks on government installations and infrastructure, including gas pipelines, over the past year.
The wedding party was travelling on a trailer being pulled by a tractor. Bugti said militants were known to have planted mines in the area and security forces had been trying to clear them.
The violence in the province, which borders Afghanistan and Iran, is another pressing security problem for Pervez Musharraf, the Pakistan president, whose forces are also battling Islamist militants in tribal areas on the Afghan border to the north of Baluchistan.
There has been no evidence or claim of any cooperation between the al-Qaida-linked Islamist rebels and the Baluch nationalists, analysts say.
"Most of the dead are women and children. Seven people were injured"
Baluchistan provincial government spokesman
Many Pakistanis - alarmed that security forces are battling their own countrymen - have criticised the government's handling of the Baluchistan trouble, saying the problem should be tackled through negotiations.
The military launched its latest crackdown on Baluch rebels after a rocket attack on 14 December during a visit by President Musharraf to the area.
Baluch nationalists say hundreds of people have been killed, but analysts say that could be an exaggeration.
The US State Department said in a human rights report this week 10 civilians were killed and more than 80 wounded in security force attacks on militants over two days at the end of December.
The government recently accused India and Afghan drug lords of meddling in Baluchistan.