Campaigners say the former Volkswagen car showroom in Iffley Road is being used as "Oxford's unofficial homeless shelter".
The site is currently home to 14 people and has been vacant for two years.
But Wadham College hopes to redevelop the building into student accommodation.
Campaigners have asked for the site to be officially designated as homeless housing.
"I don't want to see anyone freezing to death in the city that's my home," said one supporter, Miranda Shaw.
"That is something that has happened in other cities around the country and I think that is totally unacceptable."
Lewis Cairns, who is homeless and living in the squat, said: "It's a bit of a godsend really, I feel like I can get somewhere now.
"I can start applying for university and get things done."
A spokesperson for Wadham College said it was "exploring everything" and had not decided whether to take legal action.
It added its primary focus was "the safety implications for the homeless who have moved in" and said it had a longstanding relationshop with the Gatehouse homeless project.
A statement said: "The college will be making every effort to speak to representatives of this homeless group as well as local residents, safety experts and the site developers.
"As part of [redeveloping the site], Wadham College has undertaken to contribute more than Â£900,000 towards social housing provision in Oxford.
"The college regularly fundraises for homeless organisations and we donated much of the furniture from the Iffley Road site to a homeless charity."

Utopia Coaches, based at Sherburn in Elmet, North Yorkshire, provided services to rural communities between Selby, Drax, Tadcaster and York.
The company announced it was going into liquidation in a tweet on Wednesday evening, about an hour after drivers said they received the text messages.
Utopia has not responded to the BBC's request for comment.
Read more about this and other stories from across Yorkshire
Driver Carl Longfield said he left work on Wednesday with no idea the company was going to cease operating.
"I left the depot thinking everything was OK saying, 'see you tomorrow' and I got home and got a text at about 19:55 saying 'thank you very much but we are ceasing trading at 00:01'.
"We had no idea the company was in such a bad state," he said.
"The more concern for me is the passengers we have left behind in the remote communities. They relied on our services to get into work, to school, to colleges and they've been left remote."
Richard Green, another driver, said he felt completely "deflated" by the news and said he was also concerned for passengers.
"They relied on us but evidently the company couldn't be bothered about them."
The drivers met the company's liquidator earlier.
They said they were told employees would receive two weeks' pay if they had been with the company for two years or more.
North Yorkshire County Council said it was working to offer alternatives for subsidised services, including school bus services.
It added it was in discussions with other operators about whether it might be possible to restore some of the company's commercial routes.
A college that owns a building used by squatters as a homeless shelter has said it is "investigating all options", including legal action.
[NEXT_CONCEPT]
Bus drivers say they were told by text message their company was closing and they would lose their jobs.