AirHint found the following cheapest return flights from Ontario (ONT) to San Jose (SJO) in September 2025 (see full year).

Return flights

23 Sep - 07 Oct	Avianca
20 Sep - 27 Sep	Avianca
20 Sep - 04 Oct	Avianca
27 Sep - 04 Oct	Avianca
18 Sep - 22 Sep	United
11 Sep - 18 Sep	Avianca
02 Sep - 09 Sep	Avianca
13 Sep - 20 Sep	Avianca
11 Sep - 13 Sep	Avianca
06 Sep - 20 Sep	Southwest Airlines
06 Sep - 13 Sep	Avianca
06 Sep - 18 Sep	Southwest Airlines
24 Sep - 06 Oct	Southwest Airlines
23 Sep - 06 Oct	Southwest Airlines
10 Sep - 24 Sep	Southwest Airlines

Also check the deals for one-way flights from Ontario to San Jose 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.

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Cheapest return flights from Ontario to San Jose in September from $305

Return flights