Castell'Alfero () is a comune (municipality) in the Province of Asti in the Italian region Piedmont, located about east of Turin and about north of Asti.
Castell'Alfero borders the following municipalities: Asti, Calliano, Corsione, Cossombrato, Frinco, Tonco, and Villa San Secondo.
Castell'Alfero is twinned with: