The women's 400 metres hurdles at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 19 and 22 August.

Records Standing records prior to the 2021 World Athletics U20 ChampionshipsWorld U20 Record53.60Fayetteville, United States27 April 2018Championship Record54.70Kingston, Jamaica19 July 2002World U20 Leading56.74Eugene, United States12 June 2021

Results Heats Qualification: First 2 of each heat (Q) and the 2 fastest times (q) qualified for the final.

Rank Heat Name Nationality Time Note 1 1 Heidi Salminen 58.12 , 2 3 Savannah Sutherland 58.45 3 1 Ludivine Aubert 58.46 4 2 Garriel White 58.65 5 1 Angelica Ghergo 58.84 6 3 Moseiha Bridgen 58.88 7 3 Maria Tarabanskaya 59.18 8 2 Alicja Kaczmarek 59.32 9 2 Jada van Staden 59.33 10 3 Aada Aho 59.50 11 2 Ilana Hanssens 59.60 12 1 Ester Bendová 59.91 13 3 Rahela Leščak 14 2 Anna Konstantina Chatzipourgani 15 2 Neža Dolenc 16 3 Sofia Lavreshina 17 2 Andrea Švecová 18 1 Agnes Ngumbi 19 1 Lara Bezgovšek 1 Martha Rasmussen 1 Sarah Ochigbo 3 Charlize Eilerd

Final The final was held on 22 August at 15:00.

Rank Lane Name Nationality Time Note 5 Heidi Salminen 56.94 6 Ludivine Aubert 57.16 3 Savannah Sutherland 57.27 4 2 Angelica Ghergo 57.69 5 1 Maria Tarabanskaya 57.96 6 7 Alicja Kaczmarek 58.62 7 8 Moseiha Bridgen 58.64 4 Garriel White

References