In the cusp region, irregular fluctuations of the electric field are often observed by EXOS D at altitudes of several thousands of kilometers. Amplitudes of the fluctuations sometimes reach 100 mV/m and their spectra are broad. The electric to magnetic field ratios in the frequency range of 0.5--3 Hz agree well with the Alfv¿n velocity at observation point. Hence the electric fluctuations are considered to be Alfv¿n waves. The flux of precipitating ions at 500 eV to 10 keV and that of the electrons at 70--500 eV are enhanced in the cusp and they are well correlated to each other. On the other hand, correlation coefficients between the power spectral density (PSD) of the electric field at 1 Hz and the precipitating particle flux vary from case to case. When the latitude of the cusp is low and IMF is expected to be southward the coefficient is high. This suggests that the waves are generated in associated with the injection of particles into the magnetosphere when reconnection occurs. On the other hand, when the latitude of the cusp is high and IMF is expected to be northward, the coefficient is low and the PSD of the electric field is smaller for the same flux of particles than when IMF is southward. In these cases the intensity of the electric fluctuations in the region of the particle injection is possibly not so great as that when reconnection occurs. ¿ American Geophysical Union 1993