The 50 men arrived in Australia on asylum seeker boats but the Australian Government says they did not make claims that triggered Australia's refugee obligations.
It says the deportations send a clear message, "that people who pay smugglers are risking their lives and throwing their money away".
More than 380 men have been voluntarily and involuntarily sent home to Sri Lanka, since Australia's government resumed offshore processing in August.
However, 131 boats and 7600 asylum seekers have arrived during the same period.
When the processing centres on Nauru and Manus Island are complete, they will only be able to hold 2,100 people.
Meanwhile, refugee advocates say they fear asylum seekers will die while protesting on Nauru.
One man has been on a hunger strike for more than five weeks and the Refugee Action Coalition says another man collapsed on Saturday.
Spokesman Ian Rintoul says recent hot weather has made conditions in the centre worse.
"People are still in tents we're getting very close to the beginning of the wet season it is hotter and hotter, the staff find it intolerable and they get access to little air-conditioned cabins, which the asylum seekers do not," he said.
Mr Rintoul says he's worried someone will die.
"Tragically I think it is quite likely and it's not something that I say lightly, but I do think there is a very serious situation and that's why I do think it's very urgent that the minister intervenes."