Airport Fee Bangkok to ChiangMai?
 

When I fly from Australia to ChiangMai, via Bangkok (the only way possible from here), as a transit passenger in BK, will I need to pay the 500 Baht airport fee? Thanks.

No, the fee is only charged for International flights. For internal flights it is included in the ticket price.

By the way, it is not the only possible route. You could fly via Singapore, Silk Air have a direct flight to Chiang Mai.

you pay the 500 B fee when you leave bkk back to australia...

You pay as rkkwan says the 500 when leaving, so if you check in Chiang-Mai thru to Australia you pay it there or of you are not going straight thru you pay when leaving BKK.
As tangata has said Singapore Airlines thru their subsidury Silk Air have flights SIN-Chiang Mai plus also Tiger Airways from Singapore, also ( Tangata will correct me here if out of date ) Malaysia Airlines also KL-Chiang mai 'IF' they are still doing it.

Thanks for the info - it means I won't have to change money till I get to ChiangMai.
You are right, of course, about Singapore, but I really meant, there's no direct flight to ChiangMai from Sydney, as far as I know.