Winx Club: The Mystery of the Abyss (Italian: Winx Club - Il mistero degli abissi) is a 2014 Italian animated fantasy film directed and co-written by Iginio Straffi. It is the third film based on the animated television series Winx Club, and takes place after the fifth season. It follows the Winx fairies as they work to bring balance back to the Infinite Ocean after the Trix, a trio of witches, team up with a nymph named Politea to find a pearl and destroy the source of the fairies' power.

After the release of the first Winx Club movie, Iginio Straffi stated that Rainbow was "counting on" making second and third Winx films. In 2010, it was announced that Viacom, the eventual co-owner of Rainbow, would provide the resources necessary to produce the film. The Mystery of the Abyss was animated using Autodesk Maya and other programs over a period of two years.

Winx Club: The Mystery of the Abyss was released in Italy on 4 September 2014, by 01 Distribution to coincide with the series tenth anniversary. It was released theatrically in select European regions, while most international releases were televised or direct-to-video.