He was 87 and is survived by his wife, five sons and two daughters, they said.
Ko Si Mani was elected to Tamil Nadu legislative assembly from Kumbakonam constituency in 1989, 1996, 2001 and 2006.
He was the minister for co-operation between 2006 and 2011 in the DMK regime.
The DMK, in a press release tonight, asked its units in all districts to fly the party flag at half mast for three days, beginning tomorrow, as a mark of respect to the departed leader.