AirHint found the following cheapest return flights from Lisbon (LIS) to Keflavik (KEF) in September 2025 (see full year).

Return flights

19 Sep - 29 Sep	Fly Play	direct
19 Sep - 22 Sep	Fly Play	direct
29 Sep - 13 Oct	Fly Play	direct
12 Sep - 22 Sep	Fly Play	direct
29 Sep - 03 Oct	Fly Play	direct
12 Sep - 15 Sep	Fly Play	direct
15 Sep - 22 Sep	Fly Play	direct
15 Sep - 26 Sep	Fly Play	direct
13 Sep - 21 Sep	Air Europa
19 Sep - 23 Sep	Fly Play
17 Sep - 28 Sep	Aer Lingus
19 Sep - 21 Sep	Fly Play
28 Sep - 05 Oct	TAP
30 Sep - 03 Oct	easyJet
28 Sep - 05 Oct	Icelandair	direct

Also check the deals for one-way flights from Lisbon to Keflavik 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 Lisbon to Keflavik in September from $215

Return flights