At least six others were wounded in the attack. The bride, the groom and the groom's mother and sister were killed, according to the newsagency AP.
The village head of Bilge, Hamit Celebi, and 10 family members were also among the dead, Turkey's Anatolian news agency said.
NTV said the motive for the attack was thought to be a feud between rival groups of Village Guards – a controversial state-backed militia set up to combat Kurdish separatist fighters in southeast Turkey and provide intelligence.
Other reports have suggested that a "blood feud" among families had led to the killings in a region where tribal ties and rivalries sometimes eclipse the power of the state.
|Turkish media said the motive may have been a feud between rival groups in Mardin
Ahmet Ferhat Ozen, the acting governor of Mardin, told the Reuters news agency that masked men stormed into a hall where wedding guests were assembled and opened fire with automatic rifles and hand grenades.
Another unnamed witness told Reuters how the gunmen immediately began spraying the wedding hall with gunfire.
"There were a few people, they broke into the house and started spraying the place with bullets, hitting both men and women, their faces were covered with masks," the 20-year-old women said.
She said there were some 200 people at the wedding party.
Al Jazeera's Anita McNaught reporting from Istanbul, said the attack did not appear to be linked with the Kurdish separatist PKK.
Our correspondent said the use of grenades and Kalashnikov rifles seemed to be because the people involved were members of the Village Guard.
"This may be a situation where a local feud has resulted in these weapons being used on their own people," she said.
Following the attack Turkish soldiers sealed off the village, cutting off all road access, but military officials said pursuit of the attackers was being hindered by a sandstorm in the area.