The transient elastodynamic response due to concentrated normal or shear impact loads on the faces of a semi-infinite crack in orthotropic materials is examined. Solution for the stress intensity factor history around the crack tip is found. Laplace and Fourier transforms together with the Wiener-Hopf technique are employed to solve the equations of motion in terms of displacements. An asymptotic expression for the stress near the crack tip is analyzed which leads to the dynamic stress intensity factor in modes I and II. Similar to the isotropic case, it is found that the stress intensity factor has a singularity and discontinuity when the Rayleigh wave emitted from the load arrives at the crack tip. Results are presented for a typical orthotropic material.