The value from the global sightholder and auction sales dropped 5.5% from the previous cycle's $533 million and was slightly lower than the $507 million made in the seventh cycle of 2017.
It was also the lowest sales cycle volume since the tenth and last cycle of 2017, which totalled $455 million.
CEO Bruce Cleaver chalked the lower value up to the fact that some smaller, lower value rough diamonds had been sold.
"Demand remains stable ahead of the September Hong Kong Jewellery & Gem Fair," he said.
In the first six cycles of the year, De Beers sold a combined $3.4 billion worth of rough diamonds, with the total now at a provisional $3.9 billion for the year.