The Men's 100 metre butterfly S8 event at the 2020 Paralympic Games took place on 3 September 2021, at the Tokyo Aquatics Centre.

The swimmers with the top 8 times, regardless of heat, advanced to the final.

Source: [1] Archived 2021-09-25 at the Wayback Machine Source: [2] Archived 2021-09-25 at the Wayback Machine Source: [3] Archived 2021-09-25 at the Wayback Machine