  We present a detailed long-term study of the single M6 III giant RZ~Ari to
obtain direct and simultaneous measurements of the magnetic field, activity
indicators, and radial velocity in order to infer the origin of its activity.
We study its magnetic activity in the context of stellar evolution, and for
this purpose, we also refined its evolutionary status and Li abundance. In
general, for the M giants, little is known about the properties of the magnetic
activity and its causes. RZ~Ari posses the strongest surface magnetic field of
the known Zeeman-detected M giants and is bright enough to allow a deep study
of its surface magnetic structure. The results are expected to shed light on
the activity mechanism in these stars.
