The Diocese of Sisak is a Latin Church diocese in the Sisak-Moslavina region, Croatia. It is a suffragan diocese in the ecclesiastical province of the metropolitan Archdiocese of Zagreb.
Its cathedral is Katedrala Uzvišenja sv. Križa, dedicated to Exaltation of the Holy Cross, in the episcopal see of Sisak, which also has a minor basilica: Bazilika Sv. Kvirina, dedicated to saint and martyr Quirinus of Sescia, the first bishop of the diocese.