100 St Georges Terrace, Office skyscraper in Perth, Australia

100 St Georges Terrace is a 24-storey mixed retail and commercial skyscraper in Perth, Western Australia. Its office tower rises 103 metres, while the retail component, enex perth, occupies two floors of shops and food outlets between St Georges Terrace and the Hay Street Mall. The development incorporates heritage-listed facades from the earlier Hay Street buildings.

The St Georges Terrace side held a Union Bank of Australia branch from 1885, then the seven-storey New Zealand Insurance Company building in 1927 and Airways House in 1933. A 14-storey ANZ Bank opened there in November 1965, imploded on 14 July 1991. Demolition for the present tower began in February 2006, keeping heritage facades on the Hay Street Mall side.

The retail component, enex perth (formerly enex100), occupies two floors of shops and food outlets linking St Georges Terrace with the Hay Street Mall. Woolworths took a 20-year lease on 2,500 square metres of the roughly 15,000 square metres of retail space before construction began. The heritage-listed facades of the earlier Hay Street Mall buildings were kept and built into the development.

The retail floors of enex perth sit between St Georges Terrace and the Hay Street Mall, so the block can be crossed on foot through the building. A 22-bay loading dock beneath serves the shops and other Hay Street Mall retailers. The heritage facades of the earlier Hay Street buildings were kept and built into the new development.

The tower was Perth's first office building to achieve a 4.5-star Australian Building Greenhouse Rating for environmental performance. This recognition highlighted early adoption of sustainability standards that were uncommon for office buildings at that time.