Natalie Portman struggles to get her head around French etiquette rules.

The Black Swan actress moved to Paris, France in 2014 after her dancer-choreographer husband Benjamin Millepied became the Paris Opera Ballet's director of dance, but following a recent move back to Los Angeles, Natalie admits she's pleased to be back on familiar turf, as she's never really come to terms with French social customs.

"I feel there's a lot of rules of politeness and codes of behaviour there you have to follow," she said during an appearance on Jimmy Kimmel Live! on Thursday night (25Aug16). "It's a lot looser here (in the United States).

The Academy Award-winner added that Parisians have a very "cool" demeanour, and she's very careful about what how she behaves in public.

In fact, she was grateful when a friend shared some advice with her so that she wouldn't be snubbed by disgruntled staff in boutiques.

"A friend of mine taught me that when you go in some place you have to say 'bonjour' before you say anything else, then you have to wait two seconds before you say something else.

"So if you go into a store you can't be like, 'Do you have this in another size?' or they'll think you're super rude and then they'll be rude to you," she shared.

In contrast, Natalie, who has a five-year-old son named Aleph, finds Americans are a little overly friendly.

"Everyone smiles a lot here," she laughed. "It's so nice. They're more cool in France. I didn't realise I got used to it until I got here and I was so surprised. Someone would smile at my child and I'd be, 'What a good person'. People are really lovely here."