Plater College in Oxford has been bought by the international language teaching firm EF Language Schools for £5.6m.
Adult foreign students will be taught at the 267-acre campus in Pullens Lane, one of Headington's most exclusive residential areas.
The Catholic Church's decision to close and sell off the adult residential college, due to falling rolls and funding difficulties, sparked protests from ex-students and staff.
Oxford Brookes University was reported to be among the bidders after it was put on the market in February.
Until now, EF's operations in Oxford, based in London Place, have been associated with the teaching of young foreign students, aged 13 to 21.
Headington residents have expressed concern that the arrival of the language school would further change the character of the area.
Diana Chandler, chairman of the Highfield Residents' Association, said: "There's a huge amount of residential accommodation, particularly involving education and the NHS, along with office building, going on in Headington. It is changing from being predominantly made up of family neighbourhoods. "
She feared the language school would see more students "crammed in" than in the past.
Ms Chandler said: "This language school is going to mean more students and people coming and going. I'm sure there would be concern if this were to result in a large number of youths hanging around."
EF said it was too early to discuss its plans for the college.
A spokesman for the Catholic Education Service said it was setting up a committee to investigate how the proceeds of the sale could be used to fulfil "the Plater vision".
Among the ideas is a summer school to focus on the church's social teachings.