On the first altar is a glazed statue, referable to a 16th-century Venetian workshop, donated by the Tiburtine nobleman Vincenzo Leonini; on the left wall is the beautiful fresco of the Annunciation of the Virgin, dressed in white, in reference to the habit worn by the members of the Confraternity of St. John the Evangelist, who were particularly devoted to the Madonna.
On the right wall of the chancel is the Birth of St. John, and the vault and sub-arch are also decorated; in the sub-arch are the frescoes of the 12 sibyls, whose images are enclosed in medallions, and below the portrait is the prophecy of each of them.
The frescoes preserved in the single nave of the church are attributed to Florentine painter Francesco Salviati (1510-1563) and illustrate the Nativity, Crucifixion and Resurrection of Christ; other frescoes are related to the life and miracles of St. John the Evangelist.
