Abdul Ozir (45) complained of severe chest pain this morning and was shifted to the Intensive Care Unit of the hospital, where he died, they said.
A large number of relatives and friends of Ozir gathered at the hospital premises, while his brother blamed prison authorities for negligence.
As a precautionary measure, police were deployed in strength in and around the hospital and Karumbukadai area in the city, the native place of the deceased.
Ozir was arrested immediately after the blasts. He was sentenced to three life sentences under various sections, including attempt to murder and planting bombs.
The February 14, 1998 serial bomb blasts, ahead of BJP leader L K Advani's campaign meeting here, had killed 58 persons and left over 200 injured.