While female employment rates have risen in all member countries of the Organization for Economic Co-operation and Development, women still shoulder most of the burden of childcare, weighing heavily on pay prospects, the report said.
"As long as women rather than men take time off work to provide care, there will always be employers who perceive women as less committed to their career than men," said Monika Queisser, head of the OECD's Social Policy Division.
Companies are therefore less likely to invest in female career opportunities and overall pay levels for women are kept depressed, Queisser said.
The report, released to coincide with International Women's Day, said the pay gap was widest in Korea and Japan, where men earned well over 30 percent more than their female counterparts.
The next worst performers were Germany, Canada and the United Kingdom, where the pay gap was more than 20 percent, ahead of the OECD average of 17.6 percent.
Gender differences were smallest in Belgium and New Zealand, both of which had pay gaps of less than 10 percent.
The OECD said the percentage of women in work had increased to 62 percent in 2008, from 45 percent in 1970.
But women in nearly all countries spent at least twice as much time as men taking care of children or other relatives, leaving them locked into into part-time or lower status roles.
Some 25 percent of female workers opted for part-time employment, compared to 6 percent of men, the OECD report found, and women with children were more likely to adjust their working patterns than men.
