In this letter, characterization of circular High-Impedance Surfaces (HIS) is investigated. The reflection phase characterization used for rectangular HIS is here extended to circular lattices. Circular HIS discussed in this letter present a 2D periodicity and consequently the phase diagram is determined for concentric and radial polarizations. The effect of mapping a rectangular HIS into a circular one is investigated in order to give some insights regarding the design of such metasurface. The presented characterization constitutes a useful tool for the design of low-profile antennas using HIS as reflector.