| Event: | Mixed 2 x 2 × 400 metres relay |
| Competition: | 2021 World Athletics Relays |
| Goldnoc: | POL |
| Gold: | Joanna Jóźwik (W) Patryk Dobek (M) |
| Silvernoc: | KEN |
| Silver: | Naomi Korir (W) Ferguson Rotich (M) |
| Bronzenoc: | SLO |
| Bronze: | Anita Horvat (W) Žan Rudolf (M) |
| Nations: | 6 |
| Dates: | 1 May 2021 |
| Venue: | Silesian Stadium |
| Prev: | 2019 |
The Mixed 2 x 2 x 400 metres relay at the 2021 World Athletics Relays was held at Silesian Stadium on 1 May. It was the second time that this event was held at the World Athletics Relays, after being first held in 2019. Each team had to comprise one man and one woman, who would each run twice, but could be lined up in any order.[1] [2]
Prior to the competition, the records were as follows:
| World record | United States(Ce'Aira Brown. Donavan Brazier) | 3:36.92 | Yokohama, Japan | 11 May 2019 | |
| Championship record | United States(Ce'Aira Brown. Donavan Brazier) | 3:36.92 | Yokohama, Japan | 11 May 2019 |
| KEY: | WL | World leading | CR | Championship record | NR | National record | SB | Seasonal best |
| Rank | Nation | Athletes | Time | Notes | |
|---|---|---|---|---|---|
| Joanna Jóźwik (W), Patryk Dobek (M) | 3:40.92 | NR | |||
| Naomi Korir (W), Ferguson Rotich (M) | 3:41.79 | SB | |||
| Anita Horvat (W), Žan Rudolf (M) | 3:41.95 | SB | |||
| 4 | Ilona Velikanovich (W), Illia Karnavukhau (M) | 3:48.06 | NR | ||
| 5 | Dorothé Évora (W), João Coelho (M) | 3:51.69 | SB | ||
| 6 | Daniela Ledecká (W), Patrik Dӧmӧtӧr (M) | 3:54.01 | SB |