A friend has a passport from a European country. He has dual nationality and for a variety of purposes, wishes to change to a US passport (he has dual nationality). He is currently in Thailand using the European passport and has a tourist visa. In order to change over, he plans on flying to a neighboring country (probably Malaysia--KL), then returning to Thailand with the US passport. At a later date, he will be applying for a non-immigrant B visa related to work.

My question: Will he be able to enter Malaysia on one passport and leave on another, or will he have to be stamped out on the old passport?

Will he have problems entering Thailand with nothing in his new US passport even though he will arrive on a flight from Malaysia?

Anybody see any complications or have any specifics about a scenario such as this?

You must enter and leave a country using the same passport so all the stamps match. Hence you can only change passports/nationality while in the air. There is no reason your friend cannot enter Thailand with a new, unused legal US passport.

Edited June 22, 201016 yr by InterestedObserver

Thanks, I thought that was the case, but I would hate to have him run into trouble.

A related question, when my Thai wife who is dual citizen (US) moved to Thailand with me from the US in 2007 she left the US on her US passport and entered Thailand on her Thai passport. This was done she said because she was moving household goods to Thailand and needed to enter on her Thai passport. So, what should she do when we go to the US in July for a summer visit?

She always should leave and enter Thailand on her Thai passport and leave and enter the US on her US passport. The last is required by law of her.

At check-in at the airport she always shows both passports, that makes it clear that no visa is required for either countries.