The women's 4 × 400 metres relay at the 2021 World Athletics Relays was held at Silesian Stadium on 1 and 2 May.

[1] Prior to the competition, the records were as follows:[2][3] (Jania Martin, Syaira Richardson, Charokee Young, Athing Mu) Qualification: First 2 of each heat (Q) plus the 2 fastest times (q) advanced to the final.

[4] [5]