Lucas Heights is a suburb in southern Sydney, in the state of New South Wales, Australia. Lucas Heights is located 31 kilometres south-west of the Sydney central business district, in the local government area of the Sutherland Shire.

Lucas Heights is located on the Woronora River, which flows north into the Georges River. Lucas Heights is an unusual suburb in that it doesn't contain a residential area. The residential area previously part of Lucas Heights has been renamed Barden Ridge. It was renamed in 1996 to increase the real estate value of the area, so it was not instantly associated with the HIFAR nuclear reactor.

Lucas Heights is most notable for being the site of the Australian Nuclear Science and Technology Organisation (ANSTO) research establishment originally established by the Australian Atomic Energy Commission and home to the historic HIFAR research nuclear reactor. HIFAR was shut down in January 2007 and replaced by the OPAL research reactor. OPAL bears leading neutron radiation facilities and attracts international scientists as staff members and many hundreds of user groups. In the past, the HIFAR reactor was suggested a possible target for terrorist activities. The area is also visible in detail on Google Maps, which caused some concerns regarding its security.

Lucas Heights is the location of a non-nuclear waste management facility, which was for many years a major disposal site for sanitary carters. Some of the full landfills on this site are presently being sequentially redeveloped into a sporting complex containing playing fields for soccer, netball, rugby league and the home of the award-winning 'The Ridge' Golf driving range.

Menai Sand and Soil, the local landscape supplier, a pony club, and a motel are also located in the area.