The women's 400 metres T12 event at the 2020 Summer Paralympics in Tokyo, took place between 30 and 31 August 2021.

The T12 category is for athletes with visual impairment.

Athletes in this category will generally have some residual sight, the ability to recognise the shape of a hand at a distance of 2 metres and the ability to perceive clearly will be no more than 2/60.

T12 athletes commonly run with guides.

Prior to the competition, the existing records were as follows:[1] Heat 1 took place on 30 August 2021, at 20:51:[2] Heat 2 took place on 30 August 2021, at 20:59:[3] Heat 3 took place on 30 August 2021, at 21:07:[4] The final took place on 31 August 2021, at 11:36:[5]