Oxfam GB's country director in Haiti has resigned amid an inquiry into allegations of staff misconduct, the charity said.
An Oxfam spokesman said Roland Van Hauwermeiren felt he should take "managerial responsibility" because the alleged misconduct "occurred while he was heading the programme" in Haiti.
An internal investigation was launched into a "small number" of its workers in the Caribbean country. They are not thought to be British nationals.
The spokesman added that the allegations "are not connected to any incidents of fraud" and the investigation is due to be completed shortly.
The charity said the money raised following the earthquake in Haiti - approximately 98 million US dollars - has not been affected.
Oxfam has been working in Haiti since 1978. It helped about 700,000 people in the immediate aftermath of the earthquake that hit the country in January 2010.
More than 500,000 Haitians have been further assisted by Oxfam's cholera response programme.