  Despite of the importance of magnetic fields for the full understanding of
the properties of accreting Herbig Ae/Be stars, these fields have scarcely been
studied over the rotation cycle until now. One reason for the paucity of such
observations is the lack of knowledge of their rotation periods. The
sharp-lined young Herbig Ae star HD101412 with a strong surface magnetic field
became in the last years one of the most studied targets among the Herbig Ae/Be
stars.
  A few months ago we obtained multi-epoch polarimetric spectra of this star
with FORS2 to search for a rotation period and to constrain the geometry of the
magnetic field.
  We measured longitudinal magnetic fields on 13 different epochs distributed
over 62 days. These new measurements together with our previous measurements of
the magnetic field in this star were combined with available photometric
observations to determine the rotation period.
  The search of the rotation period resulted in P=42.076+-0.01d. According to
near-infrared imaging studies the star is observed nearly edge-on. The star
exhibits a single-wave variation of the longitudinal magnetic field during the
stellar rotation cycle. These observations are usually considered as evidence
for a dominant dipolar contribution to the magnetic field topology.
