Julia Roberts is storing the vintage Valentino gown she wore to the 2001 Oscars under her bed, so she can one day pass it on to her daughter Hazel.

The Pretty Woman star struck gold both in the fashion and career stakes at the Academy Awards 16 years ago, when she won Best Actress for her role in Erin Brockovich.

She accepted the prestigious accolade while modeling a black column gown with white piping and a sheer black train, and Julia admits she was lucky enough to keep the dress after the ceremony. The outfit has since been preserved, but it's being stored in a rather unlikely place.

"It's under my bed, in a box," she tells People magazine as editors named her 2017's World's Most Beautiful Woman for a record-breaking fifth time.

The designer piece is just one of many fashion picks Julia has hidden away for her little girl, hoping the 12-year-old will grow up to appreciate her mother's advance planning.

"I have this little space in my house that my husband refers to as the heritage collection," she explains. "(They're) things I go, 'I can't get rid of (this); what about Hazel?'"

Julia reveals her husband, cinematographer Danny Moder, believes Hazel may not want her mum's "old stuff", but that hasn't deterred the actress.

She adds, "I say, 'Well, maybe she'll want it'. So I keep keeping things."

But Julia won't be letting Hazel wear one of her famous red carpet gowns for her future high school prom.

"I would say, 'Don't be so dressy at the prom,'" she says. "You'd look cooler."

Julia is also mother to sons Henry, nine, and 12-year-old Phinnaeus, Hazel's twin brother.