They have occupied a floor of the university's administration building.
The students, from the Fossil Free QUB group, began their action following a winter graduation ceremony on Friday afternoon.
They claim they will "indefinitely" occupy the floor, at the rear of the 'quad' in the main Lanyon building.
The building is home to the university's finance, academic and student affairs departments.
The students are calling for the university to withdraw its investments entirely from fossil fuel corporations and to pursue a renewable energy agenda.
One of the students involved, Sean Fearon, said the university was being "intransigent" in refusing to commit to divestment.
"They have offered to review their ethical investment policy, which we see as an attempt to slow the campaign," he said.
"We want a timetable for a five-year programme for the university to withdraw any investments in fossil fuels.
"As the United Nations Conference on Climate Change is ending, it is symbolic that we've taken action to fight for our future and a cleaner planet."
He said the students planned to stay in the building until the university negotiated "properly" about their investments.
In a statement, a spokesman for Queen's said: "At its meeting on 14 October 2015, the university investment committee agreed to carry out a comprehensive review of its investment policy.
"The review is expected to take six to nine months and will be informed by best practice in the area of socially responsible investment.
"As part of this review the university has engaged directly with students of Fossil Free QUB.
"To help inform the investment policy review a workshop will be held in early January 2016 and will include students from Fossil Free QUB."

The body of the 36-year-old was found in a house in Glenfinnan Road around 15:05 on Wednesday.
Two officers were seen at the property on Friday afternoon. It was cordoned off by police tape and a bunch of flowers lay outside.
Earlier police said a post-mortem examination would be carried out to establish the exact cause of death.
They added: "A report will be sent to the procurator fiscal."

"I'm frustrated to say the least, but very pleased that we've stayed in this division," Hodges told BBC Cornwall.
"In a couple weeks time I'll be pleased we're still in this division, but we're going to have to raise the bar."
The Cornish side were safe going into their final game, which they lost 4-0 at relegated Bishop's Stortford.
"Well done for staying up," he added. "But we've underachieved by a country mile."
Having been play-off semi-finalists in 2015-16, after finishing fourth in the table, the White Tigers dropped to 19th in 2016-17, letting in 99 goals from their 42 league games, more than any other side above the bottom three.
Hodges says he will meet chairman Peter Masters this week to discuss plans for next season.
"There are a lot of decisions to be made on players," he said. "There's a few bonuses there for players who have done very well and competed, and others know that they've not been up to the standard."
About 15 students are occupying part of a Queen's University Belfast building in protest at its failure to commit to divestment from fossil fuels.
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The death of a woman in the Maryhill area of Glasgow is not being treated as suspicious, police said.
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Lee Hodges says his Truro team have underachieved by a "country mile" by finishing the season one place above the National League South drop zone.