William was welcomed by IUCN new director Inger Andersen, an expat from Denmark, at the organization's headquarters in Gland, in the canton of Vaud.
He was visiting in his capacity as patron of United for Willdlife, the foundation that he created with his wife Kate and brother Harry with the goal of protecting wildlife species threatened by poaching and illegal trafficking.
The foundation acts in concert with organizations such as IUCN and the World Wildlife Fund.
William arrived without Kate or their two children, George and Charlotte, who was born at the beginning of the month.
He flew to the Geneva airport and took a limousine 31 kilometres east to Gland, where the WWF also has its headquarters, under heavy security.
“It was very impressive, above all the security presence,” Isabelle Monney, deputy mayor of Gland, told the Tribune de Genève after meeting with the prince.
“I was able to shake his hand and say a few words about our beautiful town,” Monney said.
“He's a likeable person and above all very natural, who appreciates contact with people.”
Ricardo Tejada, communications chief for the IUCN, said William, also known as the Duke of Cambridge, took part in a series of meetings designed to fight against the illegal traffic of threatened plants and animals, the Tribune reported.
The British Embassy in Bern said the meetings were chaired by former Conservative Party leader and former UK cabinet minister William Hague.
William ate at a restaurant in the region before returning to IUCN in the afternoon, and was to leave in the evening, Tejada said.
The prince reportedly received a case of wine form the Côte region to take back home to England.