  Quasielastic scattering excitation function at large backward angle has been
measured for the weakly bound system, $^{7}$Li+$^{159}$Tb at energies around
the Coulomb barrier. The corresponding quasielastic barrier distribution has
been derived from the excitation function, both including and excluding the
$\alpha$-particles produced in the reaction. The centroid of the barrier
distribution obtained after inclusion of $\alpha$-particles was found to be
shifted higher in energy, compared to the distribution excluding the $\alpha
$-particles. The quasielastic data, excluding the $\alpha$-particles, have been
analyzed in the framework of continuum discretized coupled channel
calculations. The quasielastic barrier distribution for $^{7}$Li+$^{159}$Tb,
has also been compared with the fusion barrier distribution for the system.
