The 30-year-old beat her Black Swan co-star Mila Kunis into second place for the most page views over the past year on the TV and movie database site, which has had more than 110 million unique users in total.
Portman was awarded an Oscar for her performance in Black Swan this year, while also appearing in Thor, No Strings Attached and Your Highness.
Johnny Depp came in third place after topping the list for six of the past seven years. Emma Stone and Thor's Chris Hemsworth completed the top five.
George Clooney and Drive's Ryan Gosling also appear in the ten most searched actors, with The Dark Knight Rises actor Christian Bale coming in at number ten.
It was recently claimed that Natalie Portman was angry over director Patty Jenkins's exit from Thor 2.
> Mila Kunis: 'Acting is not an art'
The top ten stars of IMDb 2011 in full:
1. Natalie Portman
2. Mila Kunis
3. Johnny Depp
4. Emma Stone
5. Chris Hemsworth
6. Olivia Wilde
7. Jennifer Lawrence
8. George Clooney
9. Ryan Gosling
10. Christian Bale
Watch Natalie Portman and Mila Kunis in the trailer for Black Swan below: