As a kind of two-dimensional metamaterial, metasurfaces can modify the amplitude, phase, and polarization of the transmitted or reflected electromagnetic wave, and thereby can be used for enhancing the light–matter interactions. Based on this notion, an optical magnetic mirror metasurface featuring periodic nanoscale grooves is designed to confine the strong electric field near the metal surface by magnetic responses. As a result, fluorescence from an ultra-thin layer of fluorescent polymer blend (∼15 nm) on the mirror surface can be strongly enhanced (by 45-fold in experiment). The fluorescence emission can be controlled by the polarization of excitation light since the responses of the magnetic mirror are polarization sensitive. This kind of magnetic mirror metasurface is potentially useful in biological monitors, optical sources, and chemical sensors.