The trip falls on the European Union's Europe Day, which Ukraine adopted as its own on Monday, underlining its ambition to join Western institutions after applying to join the EU last year following Russia's invasion.
"Good to be back in Kyiv. "Where the values we hold dear are defended everyday," von der Leyen said on Twitter alongside a photograph of her arriving by train.
She began her highly symbolic trip shortly before Russian President Vladimir Putin marked the Soviet victory in World War Two with an annual military parade and speech on Moscow's Red Square.
Zelenskiy acted on Sunday to institute May 8 as the day Kyiv commemorates the World War Two victory -- meaning it will no longer mark it on the same day as Moscow, Ukraine's former Soviet master.
"I welcome President Zelenskiy's decision to make 9 May Europe Day also here in Ukraine," von der Leyen tweeted.
Europe Day honours a 1950 French declaration that led to the founding of the body that became the EU.
The European Commission, the EU executive, took the unusual step of publicly announcing her trip the day before she travelled. Visiting dignitaries usually keep wartime trips Ukraine secret for security reasons.
Russia has intensified its long-range attacks on targets in Ukraine as Kyiv's forces prepare to launch a counteroffensive to try to recapture Russian-occupied territory occupied in the south and east.
Russia launched at least 25 missiles overnight, with the large part of them aimed at the capital Kyiv, but nearly all of them were shot down, Ukrainian officials said.
(Reporting by Max Hunder; Writing by Tom Balmforth; Editing by Timothy Heritage)
