Abstract: For the linear adsorption isotherm, an exact solution for the prediction of breakthrough curves (step response) in fixed-bed adsorbers packed with activated carbon fiber is obtained, that takes into account axial dispersion, intrefiber diffusion and external convective mass transfer resistance. The effects of model parameters on the breakthrough curves are discussed. Two kinds of approximate solutions, i. e. , the parabolic profile approximation and the quasi -log normal distribution approximation are also obtained. The results show that the two approximate solutions are in good agreement with the exact solution over a wide range of parameters of Bi, Pe and the bed length parameter θ. The quasi -log normal distribution approximate solutionis a simple, rapid approximate solution for the calculation of breakthrough curves.