Sadleir is a suburb in south-western Sydney, in the state of New South Wales, Australia.

Sadleir is located 37 kilometres south-west of the Sydney central business district, in the local government area of the City of Liverpool.

Sadleir was part of the Green Valley housing estate, which was subdivided in 1960.

In Sadleir 54.0% of people were born in Australia, with the most common countries of birth were Vietnam 9.4%, Lebanon 6.0%, Iraq 3.2%, Fiji 1.9% and Cambodia 1.6%.

The nearest high school is in neighbouring Miller and Ashcroft, New South Wales.