European Commission chief Ursula von der Leyen said she had arrived in Kyiv with a team of commissioners on Thursday, a day before a Ukraine-European Union summit in the war-torn country.
"Good to be back in Kyiv, my 4th time since Russia's invasion.... We are here together to show that the EU stands by Ukraine as firmly as ever. And to deepen further our support and cooperation," she wrote in a tweet.
She is accompanied by 15 commissioners, including the bloc's foreign policy chief Josep Borrell.
The Commission described the visit as a "strong symbol" of European support for Ukraine "in the face of Russia's unprovoked and unjustified aggression".
EU countries have staunchly backed Ukraine since Moscow invaded in February, by hitting Russia with waves of economic sanctions and by sending weapons to Kyiv.
In June last year, Ukraine was granted EU candidate status.