This paper reports on design criteria and characteristics of a wireless ac marker that will be used for a magnetic motion capturing system capable of sensing multiple markers. The calculation of generated magnetic fields agrees with experimental result, demonstrating usefulness for designing ac markers. These simulations indicate fields as large as 0.19 A/m can be generated at 0.1 m from the marker edge by using a ferrite of 1.5 mm diameter and a layer of 72 parallel windings of 0.11 mm diameter wire, where the copper losses is close to the core losses.