To provide a foldable diving fin allowing a blade to be positively and easily fixed in a sandy beach or underwater.

In this diving fin with the blade 2 mounted to a foot side body 1 changeably into a service position and a folded position, an engaging part of claws 7, 9 for fixing the blade 2 into the service position is positioned above with a distance from the bottom face of the body 1. Even when the bottom part of the body 1 is covered with sand, the sand does not bite into the engaging part of the claws 7, 9, and even when this part is covered with sand, the sand escapes from an opening part 25 provided in a support piece 8 below. Further, the side parts of the claws 7, 9 are provided with inclined faces 24. The blade 2 can thereby be shifted sideways and fixed to the body 1.