  We report the observations of a flux rope at transition region temperatures
with the \emph{Interface Region Imaging Spectrograph} (IRIS) on 30 August 2014.
Initially, magnetic flux cancellation constantly took place and a filament was
activated. Then the bright material from the filament moved southward and
tracked out several fine structures. These fine structures were twisted and
tangled with each other, and appeared as a small flux rope at 1330 {\AA}, with
a total twist of about 4$\pi$. Afterwards, the flux rope underwent a
counter-clockwise (viewed top-down) unwinding motion around its axis. Spectral
observations of C {\sc ii} 1335.71 {\AA} at the southern leg of the flux rope
showed that Doppler redshifts of 6$-$24 km s$^{-1}$ appeared at the western
side of the axis, which is consistent with the counter-clockwise rotation
motion. We suggest that the magnetic flux cancellation initiates reconnection
and some activation of the flux rope. The stored twist and magnetic helicity of
the flux rope are transported into the upper atmosphere by the unwinding motion
in the late stage. The small-scale flux rope (width of 8.3$^{\prime\prime}$)
had a cylindrical shape with helical field lines, similar to the morphology of
the large-scale CME core (width of 1.54 $R_{\odot}$) on 2 June 1998. This
similarity shows the presence of flux ropes of different scales on the Sun.
