We used a scanning tunneling microscope to study the dynamics of step edges on the Si(001)-(2x1) reconstructed surface at temperatures from 520 to 700 K. We count changes in step edge position to determine the rates of attachment and detachment events which occur in units of four Si atoms (two dimers). Surface mass transport at these temperatures is dominated by kink diffusion. From an Arrhenius plot we find the effective activation energy for kink diffusion to be 0.97 ± 0.12 eV with a prefactor of 3x10⁵ s ^-1