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

Return flights

01 Sep - 05 Sep	Air India
01 Sep - 11 Sep	Air India
02 Sep - 07 Sep	IndiGo
09 Sep - 20 Sep	Air India
03 Sep - 08 Sep	IndiGo
03 Sep - 11 Sep	Air India
01 Sep - 07 Sep	IndiGo
17 Sep - 08 Oct	Air India
29 Sep - 09 Oct	Air India
10 Sep - 21 Sep	Air India
01 Sep - 08 Sep	IndiGo
18 Sep - 24 Sep	Air India
29 Sep - 09 Oct	SriLankan Airlines	direct
17 Sep - 08 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 357€

Return flights