  We present the first VLTI/MIDI observations of the Be star Alpha Ara, showing
a nearly unresolved circumstellar disk in the N band. The interferometric
measurements made use of the UT1 and UT3 telescopes. The projected baselines
were 102 and 74 meters with position angles of 7 degres and 55 degres,
respectively. These measurements put an upper limit to the envelope size in the
N band under the Uniform disk approximation of $\phi_{\rm max}= 4\pm1.5$ mas,
corresponding to 14 $R_{\star}$, assuming $R_{\star}$=4.8${\rm R}_\odot$ and
the Hipparcos distance of 74pc. On the other hand the disk density must be
large enough to produce the observed strong Balmer line emission. In order to
estimate the possible circumstellar and stellar parameters we have used the
SIMECA code developed by Stee (1995) and Stee & Bittar (2001). Optical spectra
taken with the echelle instrument Heros and the ESO-50cm telescope, as well as
infrared ones from the 1.6m Brazilian telescope have been used together with
the MIDI spectra and visibilities. These observations put complementary
constraints on the density and geometry of Alpha Ara circumstellar disk. We
discuss on the potential truncation of the disk by a companion and we present
spectroscopic indications of a periodic perturbation of some Balmer lines.
