Fernleigh Castle is a historic house in the Sydney suburb of Rose Bay, New South Wales, Australia.

Completed in the Victorian architectural style, the house is listed on the (now defunct) Australian Register of the National Estate[2] and the Woollahra local government heritage database.

A product of the 1890's boom, the structure is a highly decorated example of the stonemason's craft using pink to brown fine dressed sandstone, still in very good condition.

The interiors of the main rooms are very decorative contained elaborate plaster ornamentation to walls, piers and archways.

Other notable items include large tiled fireplaces framed by finely carved mahogany mantels with marble pillars supports, intricate stained glass windows, large bedroom (35ft by 18ft) three feet deep porcelain bath in cedar and marble frame, figured of white zinc.