The strain softening behavior of a particle-containing copper alloy and the associated microstructure changes were investigated as a function of strain rate (epsilon) over dot and analyzed by modeling. It is shown that, increasing strain rate (epsilon) over dot favors the multiple peak type behavior for flow stress and the appearance of strain softening behavior. During the ambient compression, the fiber structure, dislocation density and dislocation cell size and shape were also changed significantly with increasing of strain rates (epsilon) over dot. The transition from strengthening to softening was explained in terms of generation and annihilation of dislocations within dislocation cells or at cell boundaries. A new constitutive equation was developed to well describe the strain softening in the particle-containing alloy compressed at different strain rates. (C) 2010 Elsevier B.V. All rights reserved.