About 32% said same-sex marriage should be legal, while 45% said it should not be, and the remaining 23% 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% of respondents in Africa and 26% in Asia said they approved of same-sex marriage, against 35% in the Americas, 41% in Europe and 56% in Oceania the online survey found.
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.