AbstractIn this paper, we have presented the influence of precipitating energetic ions caused by electromagnetic ion cyclotron (EMIC) waves on the subauroral ionospheric E region during a geomagnetic storm on 8 March 2008 with observations of the Meteorological Operational (METOP‐02) of the Polar Orbiting Environmental Satellites (POES), a GPS receiver in Vaasa of Finland and Finnish network of search coil magnetometers. Conjugate observations of the POES METOP‐02 satellite and Finnish network of search coil magnetometers have demonstrated that enhancements of the precipitating energetic ion flux within the proton anisotropic zone are attributed to the interaction between ring current (RC) ions and EMIC waves. With enhancements of the intensity of Pc1 waves observed by search coil magnetometers, the total electron content observed by the GPS receiver accordingly increased, meaning that the enhancement of the ionospheric electron density is attributed to the precipitation of RC ions caused by EMIC waves. The electron density profiles derived by the International Reference Ionosphere (IRI‐2007) model and with precipitating energetic protons observed by the POES METOP‐02 satellite show that the energetic proton precipitation can cause the E layer peak electron density to increase from 1.62 × 109 m−3 to 5.05 × 1011 m−3 by 2.49 orders of magnitude. In comparison with the height‐integrated conductivities derived by the IRI‐2007 model, the height‐integrated Pedersen and Hall conductivities derived with precipitating energetic protons increase by 2.4 and 2.34 orders of magnitude, respectively. Our result suggests that precipitating energetic ions caused by EMIC waves can lead to an obvious enhancement of the electron density and conductivities in the subauroral ionospheric E region during geomagnetic storms.