Accurate approximate formulas are obtained for the dynamic electrophoretic mobility of a cylindrical hard colloidal particle in an oscillating electric field for two cases where the cylinder is in a transverse field or in a tangential field. These formulas, expressed in terms of Hankel functions and modified Bessel functions, are suitable for numerical calculation for all kappa a (kappa is the DebyeHuckel parameter and a is the particle radius) at zero particle permittivity and low zeta potentials. The dynamic mobility in a tangential field is shown to depend on kappa a in contrast to the static case, where it is independent of kappa a. The dynamic mobility of a cylinder averaged over a random distribution of orientation of the cylinder axis is roughly equal to the mobility of a sphere with a radius of 1.5 times the cylinder radius.