The yellow and blue symbolises the colours of the Ukraine flag.
The Church of England has called for a ceasefire and the withdrawal of Russian forces from the Eastern European country after President Vladimir Putin began his invasion this week.
The lighting up of the cathedral precedes the day of prayer for peace on Sunday (February 27).
A prayer station for residents to visit has also been set inside.
Peterborough Cathedral added: “Please pray for the people of Ukraine, for all who take decisions around the world, and for the people and leaders of Russia.