In light of Iran's censorship and repression after disputed elections in 2009, academics said they would boycott this year's event, which was scheduled for Nov. 21-23, The New York Times reported.
European countries and the United States urged Irina Bokova, UNESCO's new director general, to cancel the event.
A celebratory event scheduled for Nov. 18 in Paris now will be the main philosophy day celebration, Bokova said.
Bokova said UNESCO will not be associated with any related events in Tehran.
Diplomats and non-governmental organizations said the arrests and deportations of notable Iranian academics after the elections show the Tehran event was being driven by repressive forces in the complicated Iranian system.
World Philosophy Day started in Paris in 2002 but has been hosted in other locations such as Chile, Morocco, Turkey, Italy and Russia, with related events simultaneously in many other countries. The related events are expected to go forward this year, the Times reported.