In this work we derive exactly the two-spinon contribution to the longitudinal dynamical structure factor of the anisotropic Heisenberg spin-1/2 chain in the gapped regime by using quantum group approach. We will briefly discuss some of the mathematical difficulties when confronting form factor formulas given by quantum group approach and how to overcome these obstacles. We end up by contrasting our results with those coming from perturbation theory, while comparison to DMRG and experiments are currently underway.