The singer, who leads the chart for a fourth consecutive week, fends off competition from Far*East Movement's 'Like A G6', which remains at number two for a second week.
Nelly's 'Just A Dream' moves up a place from last week's number four to complete the top three.
Elsewhere in the Top 10, Rihanna climbs two spots from eight to six with 'Only Girl (In The World)', and Taylor Swift's new single 'Speak Now' lands at number eight.
Further down the chart, Kanye West debuts on the chart at 12 with 'Runaway', while Cee Lo Green's 'F**k You' reaches a new peak, jumping from 21 to 18.
Jay Sean leaps from 33 to 31 with his Nicki Minaj collaboration, '2012 (It Ain't The End)', and the Glee Casts' renditions of 'I Want To Hold Your Hand' and 'One Of Us' are the show's highest new entries at 36 and 37 respectively.
Pink's new single 'Raise Your Glass' enters at 51, and Edward Maya's 'Stereo Love' debuts at 93.
The top ten singles in full (click where possible for our reviews):
1. (1) Bruno Mars: 'Just The Way You Are'
2. (2) Far*East Movement Ft. Cataracs & Dev: 'Like A G6'
3. (4) Nelly: 'Just A Dream'
4. (2) Katy Perry: 'Teenage Dream'
5. (4) Usher ft. Pitbull: 'DJ Got Us Fallin' In Love'
6. (8) Rihanna: 'Only Girl (In The World)'
7. (6) Taio Cruz: 'Dynamite'
8. (*) Taylor Swift: 'Speak Now'
9. (10) Flo Rida ft. David Guetta: 'Club Can't Handle Me'
10. (7) Eminem ft. Rihanna: 'Love The Way You Lie'