The women's 400 metres T20 event at the 2020 Summer Paralympics in Tokyo, took place between 30 and 31 August 2021.

The T20 category is for athletes with intellectual impairment.

T20 athletes have an IQ score of 75 or less.

Prior to the competition, the existing records were as follows:[1] Heat 1 took place on 30 August 2021, at 20:15:[2] Heat 2 took place on 30 August 2021, at 20:22:[3] The final took place on 31 August 2021, at 20:38:[4]