Von der Leyen and Plenkovic were seen looking at euro coins newly-minted in Croatia, and Plenkovic handed over euro notes to pay for coffees for delegations of the European Commission and Croatian government.
Croatia entered the EU in 2013. It became the 27th country to join the Schengen area, and the 20th to adopt the euro currency on Sunday.
People in Zagreb said the switch to euros might make life easier, but said it would take time to get used to the change in prices. A euro was worth around 7.53 kuna just before the change came in.
Zagreb resident Pero Novakovic said it was confusing that seemingly smaller amounts of money were in fact worth more, while Snjizana Pantos said it was good that she would not have to change currencies when travelling to other eurozone countries.
Earlier, von der Leyen and Plenkovic met Slovenian President Natasa Pirc Musar at the Croatia-Slovenia border to celebrate the end of passport controls between Croatia and other Schengen countries.
Reuters