  The main goal of this work is to perform a detailed study of the optical
variability of the Be/X-ray binary SAX J2239.3+6116. We obtained multi-colour
BVRI photometry and polarimetry and 4000-7000 A spectroscopy. The optical
counterpart to SAX J2239.3+6116 is a V=14.8 B0Ve star located at a distance of
~4.9 kpc. The interstellar reddening in the direction of the source is
E(B-V)=1.70 mag. The monitoring of the Halpha line reveals a slow long-term
decline of its equivalent width since 2001. The line profile is characterized
by a stable double-peak profile with no indication of large-scale distortions.
Although somewhat higher than predicted by the models, the optical polarization
is consistent with electron scattering in the circumstellar disk. We attribute
the long-term decrease in the intensity of the Halpha line to the dissipation
of the circumstellar disk of the Be star. The longer variability timescales
observed in SAX J2239.3+6116 compared to other Be/X-ray binaries may be
explained by the wide orbit of the system.

Solar and Stellar Astrophysics;High Energy Astrophysical Phenomena