RNAS Hornsea Mere,, was a Royal Naval Air Service seaplane base located on Hornsea Mere, in the East Riding of Yorkshire, England. The mere was used for seaplanes because it was close to the sea and because its still water made it easier to launch the planes. Initially used as a relief site, the base became a full station in 1918, and was vacated in 1919. Many of the original buildings and earthworks survive.

Hornsea is a seaside town and civil parish in the East Riding of Yorkshire, England. The settlement dates to at least the early medieval period. The town was expanded in the Victorian era with the coming of the Hull and Hornsea Railway in 1864. In the First World War the Mere was briefly the site of RNAS Hornsea Mere, a seaplane base. During the Second World War the town and beach was heavily fortified against invasion.