Effects of impurities with a strong and short-range potential are studied in carbon nanotubes within a k . p scheme. The calculated conductance approaches those obtained Ibr nanotubes with a lattice vacancy when the strength of the potential is sufficiently large. The conductance at epsilon = 0 is analytically shown to be quantized into zero, one, and two times or the conductance quantum e(2)/pi (h) over bar depending on the difference in the number or vacancies at A and B sublattices in nanotubes with a sufficiently large diameter.