The Cize–Bolozon viaduct is a combination rail and vehicular viaduct crossing the Ain gorge in France connecting the communes of Cize and Bolozon in the Ain département.

An original span built in the same location in 1875 was destroyed in World War II. Reconstructed as an urgent post-war project due to its position on a main line to Paris, the new viaduct reopened in May 1950.

It carries road and rail traffic at different levels: the railway, which was closed for reinforcement and restoration in 2005, occupies the upper level. Part of the Ligne du Haut-Bugey, it reopened in December 2010 as part of the international Paris–Geneva line. The local road from Poncin to Thoirette uses the lower level.