I did copy this from the official AOT site :

"Domestic departure passengers (Airline Check-in Areas)

will be able to check-in at counters 2 and 3 on 4th floor of the departures hall. Afterwards they will have to proceed to 2nd floor to the hold room where they and their hand luggage will be security screened."

For a domestic flight, do I have to go back to the 2nd floor, after checking in at the fourth floor ? And on which floor does the actual domestic departure take place, the 2nd or 4th floor ?

All departures are on the 4th floor, then you head to the left to go through security, down some stairs/ramp, then walk to your departure gate. If you get lost there are signs.

All departures are on the 4th floor, then you head to the left to go through security, down some stairs/ramp, then walk to your departure gate. If you get lost there are signs.

Okay, thanks LucyLui. But what about this :

"Domestic departure passengers (Airline Check-in Areas)

will be able to check-in at counters 2 and 3 on 4th floor of the departures hall. Afterwards they will have to proceed to 2nd floor to the hold room where they and their hand luggage will be security screened."

Do I have to go from the 2nd floor (arrival) to the 4th floor(check-in) and then to the 2nd floor again (check hand luggage) and then finally to the 4th floor (departure domestic flight) ? This is what I read from the quoted AOT text. Where did I go wrong, if so ?

Yes, you have to go from 2nd Floor to 4th Floor to check-in BUT you head back into the main airport through security, down stairs/ramp towards the gates, turn left or right depending on your gate. Can't remember if they screen your bags again but it is straight forward. Don't always take what the AOT as gospel.

Are you arriving BKK on an international flight, and then connecting to/departing on a domestic flight? Or are you say taking a taxi to BKK and then departing on a domestic flight.

Check-in for those departing BKK is on level 4, after check-in you will clear security on the same level (back, left-hand corner) then follow the signs to your departure gate. It just so happens that the departure gate will be located on level 2, for obvious reasons, so you will go down one long escalator or two shorter ones, depending on the path you choose. It really isn't as complicated as you seem intent on making it.

Thanks !