The constitutive equation for the “elastic flexible reptating rope” model is derived. In this model the macromolecule is represented by a continuous flexible elastic rope, confined in a tube along its contour and performing a reptation motion. The analytical expressions for the relative extension and the one‐ and two‐segment distribution functions are derived. This enables the determination of the explicit form of the constitutive equation. Due to the elasticity of the rope, fast internal relaxation modes appear in the theory as well as long reptation times. It is expected that fast deformation processes can therefore be described accurately by this constitutive equation.