The Diocese of Guastalla was an Italian Latin Catholic suffragan bishopric in the province of Reggio Emilia, from 1828 to 1986.
Guastalla formed part of the diocese of Reggio until 1471, when the archipresbyterate nullius of Guastalla was territorially detached from the Roman Catholic Diocese of Reggio.
On 1585.11.05 Pope Sixtus V promoted it as Abbacy nullius of San Pietro Apostolo di Guastalla.
Only on 1828.09.13 Pope Leo XII, at the wish of Marie Louise, made it a bishopric, suffragan of the Metropolitan Archdiocese of Modena.
On 1986.09.30 it was suppressed, its territory and title merged into the thus renamed mother-Diocese of Reggio Emilia–Guastalla.
This article incorporates text from a publication now in the public domain: Herbermann, Charles, ed. (1913). "". Catholic Encyclopedia. New York: Robert Appleton.