The middle and upper atmosphere radar of Japan is a 46.5MHz, monostatic pulse-Doppler radar with an active phased-array antenna which consists of 475 crossed Yagis. Since 1983, observations of irregularities in the troposphere, stratosphere, mesosphere, and ionospheric F-region have been conducted. Here we will show that the MU radar can be used to get the electron densities of the ionospheric E-region of 90 to 160km height as well. Preliminary results are presented. We compared variations of electron density at different heights for a normal day on September 22, 1987 and for a partial eclipse on September 23, 1987. For the partial eclipse day, the electron densities in the whole E-region began to decrease at around 1030 JST. The duration was about 3 hours, and the decrease of electron density was about 20% relative to a normal day. These results showed that electron densities directly reflect the variation of the solar UV flux.