We have studied theoretically the influence of the viscous flux flow on the magneto striction for the infinite slab of type-II superconductors employing critical state model. The critical current density is chosen to be dependent on the magnetic field according to the Anderson-Kim and exponential models. The magnetostriction Delta L/L is calculated for different frequencies resulting in different viscous effects. For the field dependent critical current densities J(c)(B), we found that the presence of the viscous flux flow in the high frequencies can considerably enhance the scale of the magnetostriction curves and also alter their shape. (C) 2007 Elsevier B.V. All rights reserved.