President Vladimir Putin, the longest-serving Kremlin chief since Josef Stalin, stood beside Xi, several dozen other leaders and Russian veterans on a roofed tribune beside Vladimir Lenin's mausoleum on Red Square as Russian troops marched past.
Putin's defence minister, Andrei Belousov, inspected 11,000 troops - including many who have fought in Ukraine - and congratulated them on Victory Day to roars of approval.
The Ukraine war, Europe's deadliest since World War II, haunts this celebration.
Ukraine attacked Moscow with drones for several days this week, though there were no reports of major attacks on Russia on Friday amid a 72-hour ceasefire declared by Putin.
The Kremlin says the attendance of Russian allies such as Xi, Brazilian President Luiz Inacio Lula da Silva and several dozen leaders from the former Soviet Union, Africa, Asia and Latin America shows Russia is not isolated even if Moscow's former Western war allies stay away.
From Europe, the leaders of Serbia and Slovakia were attending.
"The victory over fascism, achieved at the cost of enormous sacrifices, has an everlasting significance," Putin told Xi in the Kremlin on Thursday.
"The countless sacrifices made by both our peoples should never be forgotten."
The Soviet Union lost 27 million people in World War II, including many millions in Ukraine, but pushed Nazi forces back to Berlin, where Adolf Hitler committed suicide and the red Soviet Victory Banner was raised over the Reichstag in 1945.
For Russians - and for many of the peoples of the former Soviet Union - May 9 is the most sacred date in the calendar, and Putin, angry at what he says are attempts by the West to belittle the Soviet victory, has sought to use memories of the war to unite Russian society.
Chinese Communist Party historians say China's casualties in the 1937-1945 Second Sino-Japanese War were 35 million.
Moscow and Kyiv do not publish accurate casualty numbers for the war in Ukraine, though US President Donald Trump, who says he wants peace, says hundreds of thousands of soldiers on both sides have been killed and injured.
Putin has sought to insulate Moscow from the grinding artillery and drone war being fought 600km away in Ukraine, though Ukrainian drone attacks have in recent days disrupted air travel to the Russian capital.
For the first time, Russia would parade drones, the biggest technological innovation of the Ukraine war, Russian state television said.
The Kremlin said the military was doing everything it could to ensure security for the parade next to the Kremlin.
Security is very tight in Moscow, as military units from 13 countries take part in the parade along with Russian troops.
Putin proposed a 72-hour ceasefire until May 10, though Ukraine said Russia had broken the ceasefire, a claim dismissed as absurd by Moscow.
