The women's 400 metres event at the 2023 European Athletics U23 Championships was held in Espoo, Finland, at Leppävaara Stadium on 13 and 14 July.

[1] Prior to the competition, the records were as follows: Qualification rules: First 3 in each heat (Q) and the next 4 fastest (q) will qualify for the semi-finals.

[2] Qualification rules: First 3 in each heat (Q) and the next 2 fastest (q) will qualify for the semi-finals.

[3] [4]