Short-range potential impurity effects on electrical conductance of nanogra
phite ribbons are investigated by means of the Landauer approach using a ti
ght binding model. In the low-energy regime ribbons with zigzag boundary pr
ovide a single conducting channel whose origin is connected with the presen
ce of edge states. The conductance as a function of the chemical potential
shows zero-conductance dip structures. This perfect reflectivity originates
from the quasi-bound states due to the potential impurity. We find that th
e conductance is sensitive to the position and strength of impurity.