The shear modulus of neutron star matter is one of the important properties
for determining torsional oscillations in neutron stars. We take into account
the effects of finite sizes of spherical nuclei on the shear modulus and
examine the frequencies of crustal torsional oscillations. The shear modulus
decreases owing to the finite-size effect, which in turn decreases the
frequencies of torsional oscillations. In particular, the finite-size effect
becomes more crucial for oscillations with a larger azimuthal quantum number
and for neutron star models with a weaker density dependence of nuclear
symmetry energy. In practice, when one identifies the quasi-periodic
oscillations from a neutron star, where the magnetic effect is negligible, with
crustal torsional oscillations, the finite-size effect can be more significant
at frequencies higher than $\sim 100$ Hz.