AirHint found the following cheapest return flights from Chicago (ORD) to Sydney (SYD) in September 2025 (see full year).

Return flights

18 Sep - 27 Oct	Frontier Airlines
17 Sep - 24 Sep	ANA
18 Sep - 25 Sep	Frontier Airlines
30 Sep - 10 Oct	Spirit Airlines
26 Sep - 29 Sep	Frontier Airlines
28 Sep - 10 Oct	Frontier Airlines
15 Sep - 20 Sep	Frontier Airlines
17 Sep - 01 Oct	Cathay Pacific
17 Sep - 23 Sep	Cathay Pacific
25 Sep - 28 Sep	Frontier Airlines
22 Sep - 26 Sep	Spirit Airlines
29 Sep - 12 Oct	American Airlines

Also check the deals for one-way flights from Chicago to Sydney in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

Book a cheap hotel in Sydney

Cheap car rent in Sydney

Cheapest return flights from Chicago to Sydney in September from $1088

Return flights