During the Winter War, the amount of Soviet Union soliders that died or went missing was five times more than Finland's.
Explanation
During the Winter War which lasted from November 3rd 1939 to March 13th 1940, the Soviet Union lost around 300,000 soldiers, both dead and missing in action, whereas Finland suffered losses of about 90,000 soldiers, including those captured and missing. This means that for every Finnish soldier who was lost, the Soviets lost roughly 3.3 soldiers.