Mr Duterte was on stage in Seoul in front of a crowd of Filipinos when he asked the audience member to kiss him in exchange for a book he was handing out.
The woman, an overseas worker who said she was married, agreed before the president leaned in to kiss her.
Mr Duterte then told the cheering crowd of about 3,000 people: “Don’t take it seriously. It’s just for fun, a gimmick.”
He said he did it to entertain his supporters – but his actions have been denounced by his critics.
Feminists have labelled the 73-year-old a misogynist following numerous jokes he has made about rape.
The controversial leader has huge domestic support and many Filipinos said they thought the kiss was harmless fun.
State-run Philippine News Agency identified the woman as Bea Kim and posted a brief video interview with her on its Facebook page.
“There wasn’t malice in it,” she said. “For me, for him, it didn’t mean anything.”
Women’s rights advocates in the Philippines recently launched an online #BabaeAko (I Am A Woman) campaign to send a message that they were not taking Mr Duterte’s “sexist” statements sitting down.
“You don’t have to kiss that woman if you want to entertain people,” said Joms Salvador, secretary-general of Gabriela
“The fact that you thought that kissing the woman would entertain people… that’s something really sick.”
Opposition Senator Risa Hontiveros said that even though the kiss was consensual, it was a “grave abuse of authority”.
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Mr Duterte has been criticised by Western governments and UN human rights officials for his anti-drug killings and threats to human rights.
More than 4,000, mostly poor, drug suspects have been killed in clashes with police that officials say erupted because the suspects fought back.