  We present B and V time series photometry of the M31 satellite galaxy
Andromeda XXVII (And XXVII) that we observed with the Large Binocular Cameras
of the Large Binocular Telescope. In the field of And XXVII we have discovered
a total of 90 variables: 89 RR Lyrae stars and 1 Anomalous Cepheid. The average
period of the fundamental mode RR Lyrae stars (RRab) $\langle$P$_{\rm
ab}\rangle$=0.59 d ($\sigma$=0.05 d) and the period-amplitude diagram place And
XXVII in the class of Oosterhoff I/Intermediate objects. Combining information
from the color-magnitude diagram (CMD) and the variable stars we find evidence
for a single old and metal poor stellar population with [Fe/H]$\sim -1.8$ dex
and t$\sim$13 Gyr in And XXVII. The spatial distribution of RR Lyrae and red
giant branch (RGB) stars gives clear indication that And XXVII is a completely
disrupted system. This is also supported by the spread observed along the line
of sight in the distance to the RR Lyrae stars. The highest concentration of
RGB and RR Lyrae stars is found in a circular area of 4 arcmin in radius,
centered about 0.2 degrees in south-east direction from Richardson et al.
(2011) center coordinates of And XXVII. The CMD of this region is well defined
with a prominent RGB and 15 RR Lyrae stars (out of the 18 found in the region)
tracing a very tight horizontal branch at $\langle V(RR) \rangle$ = 25.24 mag
$\sigma$= 0.06 mag (average over 15 stars). We show that And XXVII well
proposes as a candidate building block of the M31 halo.
