Some 32 percent said same-sex marriage should be legal, while 45 percent said it should not be, and the remaining 23 percent replied they did not know, the International Lesbian, Gay, Bisexual, Trans and Intersex Association (ILGA) survey said.
The rights group said a breakdown of the results highlighted deep regional divisions.
Only 19 percent of respondents in Africa and 26 percent in Asia said they approved of same-sex marriage, against 35 percent in the Americas, 41 percent in Europe and 56 percent in Oceania the online survey found.
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These divisions reflect that rights advocates in Africa and Asia have focused on more pressing issues, such as fighting discrimination against gays rather than promoting acceptance of same-sex marriage, said study co-author Aengus Carroll.
“This is so far off the agenda for Africa and Asia,” Carroll told the Thomson Reuters Foundation.
An ILGA survey published earlier this year found two-thirds of adults would be upset if their child told them they were in love with someone of the same sex.
Gay couples are legally recognised in more than 20 world countries, mostly in Europe and the Americas.