Final judging will take place in Brussels on May 24, with a winner announced in Nantes, the current capital, this summer.
The two British cities are vying to become the first British city to hold the title. Judges look at parks and recreational areas as well as issues of transport and energy, waste and housing.
Eight cities entered the award, launched in 2008. Glasgow’s bid champion Bailie Liz said: "This is a wonderful endorsement of everything that Glasgow is doing. In 2015, we can have a greener city, greener jobs, greener lives and a greener, better future."
Bristol mayor George Ferguson said: "We narrowly missed out on the prize last year but with determination we can do it this time round. But we need to up our game and ambition. I am determined Bristol becomes an environmental role model."
A spokeswoman for the EU, which runs the competition, said: "Three out of four Europeans live in towns and cities. Urban areas concentrate most environmental challenges facing our society but also bring together commitment and innovation to resolve them. This award has been conceived to promote and reward these efforts."