'Grenade', the follow-up to his chart-topping solo debut 'Just The Way You Are', previously spent a fortnight on top before being dethroned by Guy Sebastian 'Who's That Girl' last week.
Former Australian Idol champion Sebastian slips to two this week, while Black Eyed Peas hold steady at three with 'The Time (Dirty Bit)'.
There are no new tracks in the top ten, but notable gains outside come from Willow Smith, who advances from 22 to 18 with 'Whip My Hair, and Taio Cruz and Kylie Minogue, who leap from 39 to 25 with 'Higher'.
The top ten singles in full (click where possible for our reviews):
1. (2) Bruno Mars: 'Grenade'
2. (1) Guy Sebastian ft. Eve: 'Who's That Girl'
3. (3) Black Eyed Peas: 'The Time (Dirty Bit)'
4. (5) Katy Perry: 'Firework'
5. (4) Chris Brown: 'Yeah x3'
6. (6) Ke$ha: 'We R Who We R'
7. (7) Jessica Mauboy ft. Ludacris: 'Saturday Night'
8. (8) David Guetta & Rihanna: 'Who's That Chick'
9. (10) Pink: 'Raise Your Glass'
10. (9) Far East Movement: 'Like A G6'