Piagailoe, Coral atoll in Yap State, Federated States of Micronesia.

Piagailoe is an uninhabited atoll in Yap State, roughly 7 km long and 3.5 km wide, with a nearly circular reef ring enclosing a 5.6 km² lagoon up to 38 m deep. A shallow boat passage enters the lagoon on the southwestern reef fringe, and a side reef extends 4 km northeast. The only land is West Fayu Island, about 6 ha of dense forest at the northeast end.

The atoll lies at the western end of a chain of submarine mountains that runs about 180 km west of Gray Feather Bank, together with Condor Reef, Pikelot and Oraitilipu Bank. To distinguish it from Fayu (East Fayu) Atoll in Chuuk State, some 500 km to the east, it is also called West Fayu. Several shipwrecks lie near the atoll, a result of the shallow water and coral reefs in its immediate surroundings.

The atoll is uninhabited, so there are no local fishing communities or traditions on the reef itself. Its name West Fayu distinguishes it from Fayu (East Fayu) Atoll in Chuuk State, about 500 km to the east. Administratively it belongs to Satawal municipality, one of the legislative districts of Yap State.

Piagailoe lies 82 km northwest of Satawal, the municipality it belongs to, and 71 km northeast of Lamotrek; there is no airstrip, so access is by boat. The only landfall is West Fayu Island, about 6 ha of dense forest at the northeast end of the reef. Boats enter the 5.6 km² lagoon through a shallow passage on its southeastern side.

Piagailoe is also called West Fayu to distinguish it from Fayu (East Fayu) Atoll in Chuuk State, about 500 km to the east. The atoll marks the western end of a chain of submarine mountains running about 180 km west of Gray Feather Bank, which also takes in Condor Reef, Pikelot and Oraitilipu Bank.