Fastest 100 km ultra distance (male)
Nao Kazami
6:09:14 hour(s):minute(s):second(s)
Japan ()

The fastest 100 km ultra distance by a male athlete as sanctioned by the IAU (International Association of Ultrarunners) is 6 hours 9 minutes 14 seconds, achieved by Nao Kazami (Japan) at the Lake Saroma 100 km Ultramarathon in Kitami City, Japan, on 24 June 2018. Kazami bettered the iconic record of 6:10:20, set by Don Ritchie (UK) at the Crystal Palace athletic track in London, UK, on 28 October 1978.

As of January 2015, the IAU no longer classifies World Best Performances by surface, creating a single combined list of fastest times.