Sviatoslav Shevchuk has criticised what he has called the Vatican's "ambivalence" towards the conflict in the east of the country, and has called on Pope Francis to take a firmer stance on the problems.
Speaking to France's Catholic paper La Croix, he said: "Ukraine is in a state of shock.
"This war has already inflicted over 6,000 deaths and left 1.5 million people displaced, a quarter of them children.
"In that part of the country in the hands of pro-Russian separatists, many are dying of hunger, while our priests risk their lives daily transporting supplies.
"We understand Rome is trying to safeguard its ties with Moscow, but we also know Christ has always been on the side of those who suffer.
"In this conflict, it is Ukraine which is suffering, and the Holy See, whose diplomacy is service of the Gospel, should be at our side."
There is an official ceasefire, however there are reports of continued fighting in eastern Ukraine between Russian-backed rebels and government forces.
Archbishop Sviatoslav Shevchuk continued to say: "We would like to see a less ambivalent policy on Rome's part, and we have expressed this clearly.
"By urging respect for international law, the Holy See implicitly condemned the annexation of Crimea.
"But it did not condemn it word for word."
Catholic-Orthodox ties with Ukraine have been tense since the Moscow Patriarchate failed to openly condemn Russian aggression towards Ukraine.
