Gandhi was assassinated by a woman LTTE suicide bomber on May 21, 1991 at Sriperumbudur near here during an election rally.
Governor K Rosaiah administered the anti-terrorism day pledge to his officers and staff, the Raj Bhavan said.
TNCC President E V K S Elangovan led his partymen in remembering the late leader, adminstering an anti-terrorism pledge at the Rajiv Gandhi memorial at Sripedumbudur.
Speaking to reporters, he said terrorism was the biggest challenge to humanity and putting an end to it will benefit it.
Congress activists from across the state thronged the memorial, and took the pledge to promote the ideals of Gandhi and also fight against terrorism and communalism.