We demonstrate an all-optical switching of the magnetic resonance properties associated with a me-tallic Split Ring Resonator(SRR) array. The periodically spaced elements are fabricated on a high-resistivity silicon wafer and probed by using conventional Terahertz (THz) time-domain spectroscopy. We use a continu-ous-wave laser diode to generate carriers in the gaps of the SRR elements. Using a sufficient power, this opti-cal excitation can create an effective short gap, which would switch the resonant properties of the metamaterial from that of an SRR array to that of a closed ring resonator array and leads to dramatic changes in the THz transmission. In the present experiment, the optically induced switching is associated with the magnetic reso-nance, However, with appropriate changes in the device structure, this approach can be extended to switch a medium with a negative real index of refraction to a medium with a positive real index of refraction. This opens the way to creat a broad new range of active devices.