I would like to book as soon a One-Way flight from Phnom Penh to BANGKOK.

So, Air Asia will let me boarding without requirement like a onward ticket airplane or visa ?

Thanks by advance!

No guarentees, but normaly it is not a problem when flying in from neighbouring countries.

I've always known about this rule but have flown into Bangkok many, many times on one-way tickets. Up until my last trip I had never been asked anything from the airline, and never encountered a problem at immigration.

When flying out here last month I was questioned by EVA, and at one point they were going to make me sign a waiver, that they were not responsible for returning me if I was refused entry when arriving. Talked my way out of that one, as I knew I'd encounter no problems on the Thai end of things.

If you are asked, just tell them that you are leaving over land.