The main purpose of this paper is to present both the fundamental and some higher natural frequencies of cycloid arcs. The non-dimensional differential equations governing planar free vibrations for these arcs are derived in which the rotatory inertia is included, and solved numerically to obtain frequencies and mode shapes. Both hinged and both clamped end constraints are applied in numerical examples. The lowest four natural frequencies are reported as the functions of non-dimensional system parameters; the rise to span length ratios and the slenderness ratios. The effects of rotatory inertia on natural frequencies are reported and some typical mode shapes are also presented.