The uncle-nephew duo spend a fifth week at number one, fending off strong competition from Katy Perry's 'Last Friday Night (T.G.I.F)', which remains at two.
Elsewhere in the Top 10, Nicki Minaj's 'Super Bass' rises from four to three to become the highest-charting song by a female rapper since Missy Elliot's 'Work It' in 2002.
Meanwhile, Bad Meets Evil's 'Lighters' advances from 10 to seven and Britney Spears earns her third consecutive Top 10 hit from her Femme Fatale LP with 'I Wanna Go' at nine.
Further down the chart, Jay-Z and Kanye West's 'Otis' vaults from 47 to 12 and Drake's 'Marvin's Room' rockets 68 to 21.
Rihanna's 'Cheers (Drink to That)' lands at 91, and Black Eyed Peas' 'Don't Stop the Party' debuts at 93.
The Top 10 singles in full (click where possible for our reviews):
1. (1) LMFAO: 'Party Rock Anthem'
2. (2) Katy Perry: 'Last Friday Night (T.G.I.F)'
3. (4) Nicki Minaj: 'Super Bass'
4. (3) Pitbull feat. Ne-Yo, Afrojack and Nayer: 'Give Me Everything'
5. (6) Lil Wayne: 'How To Love'
6. (5) Adele: 'Rolling In The Deep'
7. (10) Bad Meets Evil feat. Bruno Mars: 'Lighters'
8. (7) Hot Chelle Rae: 'Tonight Tonight'
9. (11) Britney Spears: 'I Wanna Go'
10. (8) Lady GaGa: 'The Edge Of Glory'
Watch LMFAO's 'Party Rock Anthem' music video below: