Mount Ainslie, Nature reserve summit in Canberra, Australia.

Mount Ainslie is a hill of 843 metres in Canberra Nature Park, its summit topped by a small structure and an outlook over central Canberra, Red Hill and Black Mountain. The hill is an extinct Silurian volcano, about 425 million years old, made mainly of dacite and ignimbrite. A pale stone building with a central dome stands at its base.

Mount Ainslie is named after James Ainslie, a 19th-century settler and overseer of the Duntroon property, not a surveyor. In 1912 Walter Burley Griffin won the international design competition for Canberra and made the hill the northernmost point of a land axis running through the Australian War Memorial and both Parliament Houses. The Kokoda summit trail, lined with plaques about the World War II campaign in Papua New Guinea, was later laid out from the back of the War Memorial.

The Ngunnawal and Ngambri peoples regard Mount Ainslie as a sacred place primarily for women's business, and with nearby Black Mountain (Galambary) they call the two hills women's breasts. The heritage Heroes Path from the Australian War Memorial to the summit is marked by plaques describing the Kokoda Track campaign of the Second World War. Weekly community events include the Mount Ainslie Run-Up and a Saturday parkrun on the bush trails along the park's western edge.

The paved Kokoda summit trail starts behind the Australian War Memorial, climbs via steps and is used by about 200 people daily. A road also reaches the summit. A quarry lies about 200 metres from the peak. The summit outlook faces central Canberra, Red Hill and Black Mountain, and is popular towards sunset.

The summit beacon is a rotating air navigation light guiding traffic to Canberra Airport. The peak also marks the northern end of the land axis Walter Burley Griffin planned in 1912, running through the Australian War Memorial and both Parliament Houses. In 2013 the summit view was named after his wife, Marion Mahony Griffin.