West Moncoeur Island, Nature reserve in Bass Strait, Tasmania, Australia.

West Moncoeur Island is a granite island of 9.18 ha in the Rodondo Group, northern Bass Strait, about 14 km from South Point on Wilsons Promontory. Its coastline is cut by cliffs and gullies shaped by wind and waves, and two rock formations have split off from the main island, forming a rocky barrier around it.

Lieutenant James Grant of HMS Lady Nelson sighted the island on 9 December 1800 during his first voyage to Australia and named it after Captain Moncur of the Royal Navy. The Rodondo Group, including West Moncoeur, remained largely unvisited because of difficult access; John Béchervaise's expedition carried out the first sustained surveys, spending over a week on Rodondo itself while only briefly observing the Moncoeur islands. The island was declared a nature reserve on 6 December 1978.

The island's name honours Captain Moncur of the Royal Navy, recorded by James Grant in December 1800 during the Lady Nelson's first voyage to Australian waters. The Rodondo Group long went unvisited because of difficult access; only John Béchervaise's expedition made the first sustained studies, spending over a week on Rodondo itself while the Moncoeur islands were surveyed only briefly.

Landing is effectively impossible: a ring of granite cliffs and gullies surrounds the island, and two rock formations have already split away from it. The Rodondo Group went long unvisited because of this inaccessibility, and John Béchervaise's expedition surveyed Rodondo itself over more than a week but only viewed the Moncoeur islands from offshore. Detailed study came later through aerial and satellite imagery.

The island holds a breeding colony of Australian fur seals where about 250 pups are born each year. The granite shore and surrounding reefs also shelter metallic skinks, and the island lies within the Wilsons Promontory Islands Important Bird Area, identified by BirdLife International for its breeding seabirds.