Mastalus I (Italian : Mastalo) (died 953) was the penultimate patricius of Amalfi. He was succeeded by his son, Mastalus II, who was raised to the status of dux . His own father was the last prefect, Manso I.
In 946, he came to the rescue of Gisulf I of Salerno, who was assaulted by an alliance of Landulf II of Benevento and John III of Naples. Mastalus ambushed Landulf's forces in the pass at La Cava.