The United Nations agency, marking International Women's Day, says negative stereotyping undermines the education of girls, according to the BBC.
It says too often female figures are represented in textbooks as "nurturing drudges" in domestic roles.
This is a "hidden obstacle" to gender equality, says UNESCO's Manos Antoninis.
UNESCO has campaigned to provide education for tens of millions of children without access to school - and in many poorer countries girls are the most likely to miss out.
This report highlights how female characters frequently appear in a secondary role in the books they use at school – and warns that it limits girls' career expectations.
"Ensuring all boys and girls go to school is only part of the battle," says Manos Antoninis, from UNESCO's global education monitoring report.