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

Return flights

01 Sep - 04 Sep	Air India
02 Sep - 05 Sep	Air India
06 Sep - 14 Sep	Air India
14 Sep - 21 Sep	Air India
28 Sep - 05 Oct	Air India
07 Sep - 15 Sep	Air India
21 Sep - 29 Sep	Air India
05 Sep - 14 Sep	Air India
11 Sep - 14 Sep	Air India
08 Sep - 17 Sep	IndiGo
20 Sep - 28 Sep	Air India
27 Sep - 04 Oct	Air India
28 Sep - 05 Oct	SriLankan Airlines	direct

Also check the deals for one-way flights from Kathmandu to Colombo 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 Kathmandu to Colombo in September from 344€

Return flights