Sydney has slipped in an international assessment of liveability, ranking behind other Australian capitals Melbourne, Adelaide and Perth.

The NSW capital has dropped from seventh to 11th place in The Economist Intelligence Unit's Global Liveability Report 2017.

Sydney has slipped in the Global Liveability Ranking. Credit:Sandra Jackson

The study attributed Sydney's fall to escalating fears about terrorism.

"Sydney in Australia is another city that has seen a decline in its ranking, reflecting growing concerns over possible terror attacks in the past three years," the report stated.