The basic structure of the 2,000-year-old site was intact, Syria's antiquities chief was quoted as saying.
But UN satellite analysts Unosat say the image shows almost nothing remains.
"Unfortunately, the images we acquired do show that the main building of the temple has been destroyed," reported BBC citing Einar Bjorgo, Unosat's manager as saying.
He added that a set of columns nearby had also been destroyed.
The group have also recently destroyed another major ruin in the city, the Baalshamin temple. The satellite images show the extent of the damage to Baalshamin. The ancient city of Palmyra was captured by ISIS militants in May this year.
The Temple of Bel is dedicated to the Palmyrene gods and was one of the best-preserved parts of the ancient city.