The attack on Tuesday came on the eve of a visit to the country by George Bush, the US president, and was one of the biggest by Maoists in recent years.
S K Paswan, a senior police officer, said: "Maoists set off a landmine in Darmagura area in Dantewada district, killing 55 people."
The dead were tribal members returning in trucks after attending an anti-Maoist meeting organised by the state, he said.
Ram Vichar Netam, the state's home minister, said 20 people had been seriously wounded and the toll could rise.
Darmagura, 500km south of the state capital Raipur, is a stronghold of Maoists who say they are fighting for the rights of peasants and landless labourers.
Indian Maoists, who operate in at least nine of the country's 29 states, have stepped up attacks in the past year, killing dozens of people including police.
Security analysts say New Delhi has not taken the Maoist threat in the country seriously.
India's Home Ministry has said there are about 9300 Maoist guerrillas operating in the country.