Michael Bay's robot sequel pulls in £4 million less than last week, but its final total is still enough to secure the top spot ahead of The Hangover.
New releases Year One and My Sister's Keeper enter the chart at number three and four respectively, while Night At The Museum 2 rounds out the top five.
Elsewhere, anime adaptation Blood: The Last Vampire opens at number seven, Kabir Khan's Bollywood film New York is at nine and Sunshine Cleaning lands at ten.
The UK box office top ten in full:
1. (1) Transformers: Revenge Of The Fallen - £4,368,024
2. (2) The Hangover - £1,910,025
3. (-) Year One - £978,008
4. (-) My Sister's Keeper - £922,947
5. (3) Night At The Museum 2 - £492,990
6. (4) Terminator Salvation - £424,277
7. (-) Blood: The Last Vampire - £232,190
8. (5) Angels & Demons - £166,253
9. (-) New York - £157,524
10. (-) Sunshine Cleaning - £125,795