27 people, including three scientists, were taken ill at the Indian Science Congress venue at the Annamalai University in Chidambaram, 235 kilometres from Chennai.
All the affected persons had eaten on Tuesday at the food court set up by the university at the venue, the police said.
They started vomiting late in the night and were immediately rushed to the Raja Muttiah Medical College Hospital where they were treated for food poisoning.
While 24 of them were treated as outpatients, three police personnel were admitted to the hospital, the police added.
Over 5,000 delegates from India and abroad are attending the ISC, to be inaugurated by Prime Minister Manmohan Singh on Wednesday.