The gruesome video shows hundreds of supporters of the militant group gather in the city of Raqqa.
The three terrified soldiers can be seen on their knees shortly before the enormous crowd is allowed to surround the men.
They begin kicking, stamping and punching the trio while children watch on.
At one point, the crowd is about a dozen deep with ISIS supporters desperate to join in the beating, Mail Online reported.
After the men are beaten to death, the video shows their corpses being dragged through the city's streets from motorbikes.
ISIS militants can be seen following behind in vehicles, cheering and sounding their horns.
The Syrian Observatory for Human Rights said the three men were captured from the village of Ratyan.