The 2017 UCI Mountain Bike World Championships was the 28th edition of the UCI Mountain Bike World Championships. As in 2016, the championships in the various disciplines were held at separate events. The world championships in four-cross were held at Val di Sole, Italy, on 24 and 25 August 2017, alongside UCI World Cup events in cross-country and downhill. The world championships in cross-country and downhill were held in Cairns, Australia, from 5 to 10 September 2017.