Police said the crime took place in the Tinsukia-bound Bangalore-Tinsukia Express on Thursday night.
"The young woman, who works as a domestic help in Bengaluru, was returning home in Tinsukia ahead of Durga Puja. Most passengers travelling in a particular compartment alighted at Dibrugarh station on Thursday night. The three youth travelling in the compartment later took the woman to the train toilet and raped her," the police said.
After the train reached New Tinsukia station on Friday morning, the woman narrated the incident to her brother who had come to the station to receive her.
He informed the Government Railway Police at the station, after which one accused was held.
The woman later lodged a formal complaint against the three youths.
Police said the arrested youth, Prahlad Chhetri, confessed to his involvement in the crime but maintained that the other two were not involved.
