Rights group say female refugees are particularly vulnerable to exploitation by landlords and employers.
Ninette Kelley, the U.N. refugee agency's representative in Lebanon, said the agency has received over 500 cases of women who have been sexually abused or exploited in Lebanon.
"But we know that those numbers aren't entirely accurate because there's a lot of taboo against coming forward and expressing these incidents and these risks in the open," she said in an interview.
Human Rights Watch said it interviewed a dozen women for the report, who described being groped, harassed, and pressured to have sex. Eight of the women are widowed, unmarried, or in Lebanon without their husbands. All 12 women are registered as refugees with UNHCR, it said.
One of them, a woman from Damascus identified by her first name Hala, said she suffered sexual harassment or attempted exploitation in nine of the 10 households in which she had worked in a Beirut suburb to support herself and her four children.
Hala said she now rejects job offers and depends on a church for aid. She said she did not report the incidents to Lebanese authorities or the UN because she did not believe they would help her.
"Government and aid agencies need to open their eyes to the sexual harassment and exploitation of these vulnerable refugees and do everything in their power to stop it," Gerntholtz said.