Guido III da Polenta (died 1389) was a lord of Ravenna, Italy and a member of the da Polenta family.
He peacefully held the city's government for 30 years after the death of his father, Bernardino I. Guido married the daughter of Obizzo III d'Este of Ferrara, Elisa d'Este, who gave him numerous children. Most of the daughters married other lords of Romagna and northern Italy.
In 1389 he was imprisoned by his sons Bernardino, Ostasio, Obizzo, Aldobrandino, Azzo and Pietro, and died in jail.
| Preceded by Bernardino I | Lord of Ravenna 1359–1389 | Succeeded by Obizzo da Polenta and his brothers |