Mushroom kingdom. He doesn't exist in the real world so I'd assume he has no real world nationality.

Italian i guess

His not Mushroomian because he wasnt born in the Mushroom kingdom from my memory. His American with a Italian background.

I am so surprised people are choosing Italian. He is a Japanese symbol, made by a Japanese company. Even Nintendo themselves have dissociated him from his early Italian identity. As a fictional character, he belongs culturally to the people that created him - therefore he is a Japanese figure. Even if we were to use his past, Mario hasn't been "Italian" for a very long time now. Aside from the funny "Italian" accent, his Italian identity has been superseded long time ago now.

He is italian, but we are talking about another dimension, not ours.

You can't just strip someone of their past. Not matter how muck you hide it there is always someone that will use it to blackmail you.

Personally, I've (I think always) viewed him as an American Plumber with a fake Italian accent that he uses for kicks and giggles.

Well, as they say, "Brooklyn Mario is better than Italian stereotype Mario."

I agree. So, American of Italian descent.

I figured it was some sort of Jewish sterotype which is why he's searching for gold coins.

Terrible jokes aside, he's an Italian American. His grand father is probably an immigrant and WWII veteran. Mario's father was also veteran of Viet Nam and started a plumbing business when he returned. Now his two sons run the business. This is where the movie will start...

Italian.