The Men's 100 metre butterfly swimming events for the 2020 Summer Paralympics took place at the Tokyo Aquatics Centre from August 25 to September 3, 2021.
The S8 category is for swimmers who have a single amputation, or restrictive movement in their hip, knee and ankle joints.
The final in this classification took take place on 3 September 2021: The S9 category is for swimmers who have joint restrictions in one leg, or double below-the-knee amputations.
The final in this classification took place on 2 September 2021: The S10 category is for swimmers who have minor physical impairments, for example, loss of one hand.
The final in this classification took place on 31 August 2021: The S11 category is for swimmers who have severe visual impairments and have very low or no light perception, such as blindness, they are required to wear blackened goggles to compete.