A wireless microphone includes a perforated front cover mounted on a front open end of a tubular housing, and a control module mounted fixedly on a rear open end of the housing and having an outer surrounding surface provided with a power switch and electrode plates. A rear cover is connected detachably to the control module, and is formed with a switch-receiving groove and through holes. The rear cover is operable so as to be disposed between an adjusted position, where the power switch is exposed from the switch-receiving groove and where the electrode plates are respectively exposed from the through holes, and a used position, where the power switch and the electrode plates are fully covered by the rear cover. A positioning member positions the rear cover at a selected one of the used and adjusted positions.