AirHint found the following cheapest return flights from Colombo (CMB) to Kathmandu (KTM) in September 2025 (see full year).

Return flights

15 Sep - 18 Sep	Air India
19 Sep - 27 Sep	Air India
19 Sep - 03 Oct	Air India
22 Sep - 05 Oct	Air India
17 Sep - 15 Oct	Air India
20 Sep - 03 Oct	Air India
22 Sep - 22 Oct	Air India
24 Sep - 22 Oct	Air India
21 Sep - 29 Sep	Air India
18 Sep - 02 Oct	Air India
24 Sep - 24 Oct	Air India
27 Sep - 27 Oct	Air India
29 Sep - 29 Oct	Air India

Also check the deals for one-way flights from Colombo to Kathmandu 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 Colombo to Kathmandu in September from 375€

Return flights