Sant'Eustachio (Italian: [santeuˈstaːkjo]) is the 8th rione of Rome, Italy, identified by the initials R. VIII.

Its coat of arms depicts the head of a stag with a cross between the antlers, symbol of Saint Eustace: the figure is golden on a red background.

Northward, Sant'Eustachio borders with Campo Marzio (R. IV), whose boundary is defined by Piazza in Campo Marzio, Via della Stelletta and Via dei Portoghesi.

To the west, the rione borders with Parione (R. VI), from which is separated by Piazza delle Cinque Lune, Corso del Rinascimento, Corso Vittorio Emanuele II, Largo dei Chiavari and Via dei Chiavari.

Southward, Sant'Eustachio borders with Regola (R. VII), the boundary being outlined by Via dei Giubbonari, Piazza Benedetto Cairoli, Via Arenula and Via di Santa Maria del Pianto; as well as with Sant'Angelo (R. XI), from which is separated by Via in Publicolis, Via dei Falegnami, Via di Sant'Elena and Largo Arenula.