I am holder of EU passport containing extension of Non Imm "O" visa.

End of October I will return to Thailand with a new passport issued by the city hall where I live.

Which passport details should I mention on the arrival card : the old (cancelled) one with the Thai Non Imm "O" extension, but still having a few empty pages... or the new blank passport ?

I am concerned that seeing the new blank passport I will from get Immigration at arrival an entry stamp for only one month which is given to EU tourists.

Your old one will have something on it that says cancelled, so you can't use that one. Show him your new passport and your old one. Make sure you have a reentry permit before you leave. When you come back I believe they will transfer your old visa to your new passport, and you will have to get a new extension, I don't know if you can do that at the airport or your regular immigration office. I'm guessing but I think they will stamp you in for 30 days and then you will have to get an extension.

Your old one will have something on it that says cancelled, so you can't use that one. Show him your new passport and your old one. Make sure you have a reentry permit before you leave. When you come back I believe they will transfer your old visa to your new passport, and you will have to get a new extension, I don't know if you can do that at the airport or your regular immigration office. I'm guessing but I think they will stamp you in for 30 days and then you will have to get an extension.

Seems he's in Europe now. So, unless he obtained a re-entry permit prior to leaving Thailand, the only course of action open to him would be to trot along to his local Thai consulate or Embassy with his new passport and obtain a fresh non-O visa.

That's right, fvw53 Without a re-entry permit in the old passport, the extension of stay lost its validity the day you left Thailand.

If you have a re-entry permit, put the number of your new passport on the arrival card and the re-entry number in the space for the visa number, then give the immigration officer both passports and tell him that you got a new passport while you were in {country name}. Be sure to give the country name, not say EU as you did in your post, because it is not the EU issuing your passport and you don't want to confuse the officer.

thanks for the helpful suggestions / yes I still have a valid multiple re-entry visa in the old passport

thanks for the helpful suggestions / yes I still have a valid multiple re-entry visa in the old passport

I assume you actually mean "valid multiple re-entry permit". You'll need to enter the number of this permit in the "Visa No." boxes on the TM6 arrival card you'll be handed during your return flight, and not your latest extension of stay number.

thanks for the helpful suggestions / yes I still have a valid multiple re-entry visa in the old passport

I assume you actually mean "valid multiple re-entry permit". You'll need to enter the number of this permit in the "Visa No." boxes on the TM6 arrival card you'll be handed during your return flight, and not your latest extension of stay number.

Yes you are right : I should have written "re-entry permit" - thanks again