Abu Dhabi provided direct and indirect injections totaling $25 billion last year as Dubai’s debt problems deepened.
The tower was revealed to be 828m (2716ft) high, far taller than the previous record holder, Taipei 101.
Clad in 28,000 glass panels, it has 160 floors and more than 500,000 sq m of space for offices and apartments.
Construction began in 2004, at the height of an economic boom. But the opening follows a financial crisis which saw Abu Dhabi bail out Dubai.
At 828m, Burj Dubai dwarfs the 508m Taipei 101 and the 629m KVLY-TV mast in the US, the tallest man-made structure. Its spire can been seen 95km (60 miles) away.
Though not complete on the inside, Burj Dubai (Arabic for tower) was officially opened by Dubai’s ruler
Burj Dubai will be home to 1,044 luxury apartments, 49 floors of offices and eventually a 160-room Armani-branded hotel. Around 12,000 people are expected to live and work in the tower, which is part of a 500-acre development.
However, investors are facing losses even before the tower is completed because property prices in Dubai have slumped amid the global economic crisis.
Some apartments were selling for $2,700 per sq ft, but are now going for less than half that.