2021 World Athletics Relays – Mixed 4 × 400 metres relay

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

Records
Prior to the competition, the records were as follows:

Heats summary
Qualification: First 2 of each heat (Q) plus the 2 fastest times (q) advanced to the final.


 * {{legend|ccffcc|Q Qualified}}
 * {{legend|ccffcc|q Qualified as fastest times}}
 * WL = World leading
 * NR = National record
 * SB = Seasonal best
 * OG* = 2020 Olympic Games qualification
 * WC* = 2022 World Championships qualification

Final
Italian national track relay team confirms the first place obtained in the heats summary.