The Duchess of Cambridge and husband Prince William recently completed their first overseas state visit as a married couple, spending 12 days in North America.
Fashion Police star Rancic told Digital Spy that she had been impressed with how the Duchess dressed on the visit, particularly in light of the intense scrutiny she was under and the numerous outfits she wore each day.
"I think it's hard to have to dress knowing the whole world will look at you and judge you, but she is doing an excellent job of dressing sophisticated and elegant but still young in her colour choices and silhouettes," she said.
"I think she did an incredible job, especially in Canada and the US when she had so many outfits to wear and was changing maybe two or three times a day. There was definitely a lot of pressure on her but I think she looked absolutely beautiful and flawless."
The E! News host also noted her personal preference on the Duchess's hairstyle, saying: "I like her when she has her hair down more than pulled back; she has a gorgeous head of hair which should always be left down to blow in the wind."
Rancic can be seen opposite husband Bill in the new season of Giuliana & Bill, which premieres tonight at 9pm on Style.
> Giuliana Rancic talks babies, pet peeves and "flawless" Kate Middleton
> Bill Rancic talks year of fun with Giuliana, restaurant plans and Apprentice