The Diocese of Nicopolis[b] (Latin: Dioecesis Nicopolitanus) is a Latin diocese of the Catholic Church, which includes the whole northern part of Bulgaria.

The seat of the episcopal see is in Rousse, although the diocese is named after Nicopolis ad Istrum.

The diocese is immediately subject of the Holy See.

The current bishop is Strahil Kavalenov.

[1] Originally erected in 1789, the diocese has not experienced any name changes, nor jurisdictional alterations.