Cattai National Park, Nature reserve in The Hills Shire Council, Australia.

Cattai National Park covers 424 hectares on the Hawkesbury River about 55 km northwest of Sydney, in three parts: Cattai Park at the junction with Cattai Creek, Hope Farm adjoining it to the north, and Mitchell Park about 2.5 km upstream along the creek. The park holds a homestead built around 1820, ruins of a stone windmill thought to be Australia's oldest industrial building, and convict-built dry stone walls.

The park occupies land granted to Thomas Arndell, assistant surgeon of the First Fleet. His farmhouse, Cattai Homestead, was built around 1820 and is listed by the National Trust and the Australian Heritage Commission. Hope Farm Mill, probably built around 1806, is thought to be Australia's oldest industrial building. Convict-built dry stone walls also remain.

The park's name comes from Cattai Creek, and the land was part of a grant to Thomas Arndell, assistant surgeon of the First Fleet, whose 1821 farmhouse still stands in the park. Aboriginal sites in the park document how the Cattai area was used before European settlement.

The park has three separate sections: Cattai Park at the junction of Cattai Creek and the Hawkesbury River, Hope Farm adjoining it to the north, and Mitchell Park about 2.5 km upstream along Cattai Creek. Picnic areas are available, and the homestead can be visited. Camp only in designated areas and do not feed the wildlife.

The park preserves dry stone walls built by convicts during the early colonial period that are still visible today. These walls represent the labor and craftsmanship of that era and are recognized as part of Australia's heritage.