More than 100,000 voted in the survey, which asked Digital Spy users to pick their favourite movies, music, gaming, tech and showbiz highlights from the past 12 months.
The Black Swan star topped the reader voting ahead of Harry Potter's Emma Watson and The King's Speech's Helena Bonham Carter.
Bridesmaids star and co-writer Kristen Wiig is at number four, while Emma Stone ranks at number five ahead of Twilight's Kristen Stewart.
2011 also saw Portman win the 'Best Actress' Oscar for her role as a psychologically-tortured ballerina in Black Swan and give birth to her first child, Aleph Portman-Millepied, in June.
Digital Spy readers' top 10 actresses of 2011 are:
1. Natalie Portman
2. Emma Watson
3. Helena Bonham Carter
4. Kristen Wiig
5. Emma Stone
6. Kristen Stewart
7. Mila Kunis
8. Tilda Swinton
9. Jennifer Aniston
10. Michelle Williams
Watch Natalie Portman in the trailer for Black Swan below: