Phone: þ98 741 222 3048, Fax: þ98 741 222 3048In the present work, the linear and the third-order nonlinear optical absorption coefficients as well as refractive-index changes in a two-dimensional hexagonal quantum dot with the presence of an impurity are calculated. A matrix diagonalization method is used to calculate energy levels and corresponding wave functions in the effective-mass approximation. Also, by means of the compact-density matrix approach the linear and nonlinear optical absorption coefficients and refractive-index changes are calculated. The effects of the impurity, the size of the dot and the confinement potential on energy eigenvalues, optical absorption coefficients and refractive-index changes are investigated. It is found that the energy eigenvalues, absorption coefficients and refractiveindex changes are strongly dependent on the dot size, the confinement potential and the effects produced by the impurity.